HK1131463B

HK1131463B - Mass spectrometer

Info

Publication number: HK1131463B
Application number: HK09111172.8A
Authority: HK
Inventors: 罗伯特‧哈罗德‧巴特曼; 杰弗里‧马克‧布朗; 马丁‧格伦; 詹森‧李‧维尔德古斯; 安东尼‧詹姆斯‧吉尔伯特; 史蒂文‧德里克‧普林格尔
Original assignee: 英国质谱公司
Priority date: 2006-06-01
Filing date: 2007-06-01
Publication date: 2012-01-06

Description

Mass spectrometer

Technical Field

The present invention relates to a mass spectrometer and a method of mass spectrometry.

Background

One known method of obtaining mass spectra is to record the output signal from an ion detector of a mass analyser as a function of time using a fast analogue to digital converter (ADC). It is known to use an analog to digital converter with a scanning magnetic sector mass analyser, a scanning quadrupole mass analyser or an ion trap mass analyser.

In the case where the mass analyser is scanned very quickly for a longer period of time (for example, scanning the mass analyser very quickly over the entire duration of a chromatographic separation experimental run), it is clear that a very large amount of mass spectral data will be acquired if an analogue to digital converter is used. Storing and processing large amounts of mass spectral data requires large memories, which is disadvantageous. In addition, the large amount of data has the effect of slowing down subsequent data processing. This can be particularly problematic for real-time applications such as Data Dependent Acquisition (DDA).

Due to the problem of using an analog-to-digital converter with a time-of-flight mass analyser, a time-to-digital converter (TDC) detector system is typically used instead with a time-of-flight mass analyser. Time-to-digital converters differ from analog-to-digital converters in that time-to-digital converters only record the time at which ions are recorded as arriving at an ion detector. Thus, the time-to-digital converter produces significantly less mass spectral data, which makes subsequent data processing significantly easier. However, one drawback of time-to-digital converters is: they do not output the intensity values associated with the ion arrival events. Thus, the time-to-digital converter cannot distinguish between one or more ions arriving at the ion detector at substantially the same time.

Conventional time-of-flight mass analyzers sum ion arrival times determined from multiple acquisitions by a time-to-digital converter system. No data is recorded at the time no ions arrive at the ion detector. A composite histogram of the recorded times of ion arrival events is then formed. As more and more ions are added to the histogram from subsequent acquisitions, the histogram is stepped up to form a mass spectrum of ion counts versus time of flight (or mass-to-charge ratio).

Conventional time-of-flight mass analyzers can collect, sum or histogram hundreds or even thousands of individual time-of-flight spectra obtained from each individual acquisition in order to produce a final composite mass spectrum. The mass spectrum or histogram of ion arrival events may then be stored to computer memory.

One drawback of conventional time-of-flight mass analyzers is: many individual spectra that are histograms processed to produce the final mass spectrum may be associated with an acquisition that records only a few ion arrival events or no ion arrival events. This is particularly true for orthogonally accelerated time-of-flight mass analyzers that operate at very high acquisition rates.

Known time-of-flight mass analysers comprise an ion detector comprising a secondary electron multiplier such as a microchannel plate (MCP) or a discrete dynode (dynode) electron multiplier. A secondary electron multiplier or discrete dynode electron multiplier generates a pulse of electrons in response to ions arriving at the ion detector. The electronic or current pulses are then converted into voltage pulses, which can then be amplified using a suitable amplifier.

State of the art microchannel plate ion detectors can generate a signal in response to the arrival of a single ion, where the signal has a full width at half maximum of 1ns to 3 ns. Ion signals are detected using a time-to-digital converter (TDC). If the signal generated by the electron multiplier exceeds a predetermined voltage threshold, the signal may be recorded as being related to an ion arrival event. Ion arrival events are recorded only as time values without associated intensity information. The arrival time is recorded as the time corresponding to the leading edge of the ion signal passing the voltage threshold. The recorded arrival time will be accurate only to the most recent clock step of the time to digital converter. State of the art 10GHz time-to-digital converters are capable of recording ion arrival times to within ± 50 ps.

One advantage of using a time-to-digital converter to record ion arrival events is: by applying a signal or voltage threshold, any electronic noise can be effectively removed. Therefore, if the ion current is small, no noise is present in the final histogram mass spectrum and a good signal-to-noise ratio can be achieved.

Another advantage of using a time-to-digital converter is: the analog width of the signal generated by a single ion is not added to the width of the ion arrival envelope for a particular mass-to-charge ratio value in the final histogram mass spectrum. Since only ion arrival times are recorded, the width of the mass peaks in the final histogram mass spectrum depends only on the spread in ion arrival times for each mass peak and the variation in the height of the voltage pulse generated by the ion arrival event relative to the signal threshold.

However, one important disadvantage of conventional time-of-flight mass analyzers that include ion detectors that include time-to-digital converter systems is that: time-to-digital converters cannot distinguish between signals due to a single ion arriving at the ion detector and signals due to multiple ions arriving at the ion detector simultaneously. The inability to distinguish between single and multiple ion arrival events results in intensity distortion of the final histogram or mass spectrum. In addition, ion arrival events will only be recorded if the output signal of the ion detector exceeds a predetermined voltage threshold.

Known ion detectors incorporating time-to-digital converter systems also suffer from the following problems: it exhibits a recovery time after an ion arrival event is recorded during which time the signal must fall below a predetermined voltage signal threshold. During this dead time (dead time), no ion arrival events can be recorded anymore.

At larger ion currents, the probability of several ions arriving at the ion detector substantially simultaneously during one acquisition may become considerable. Thus, dead time effects will cause distortion of the intensity and mass-to-charge ratio locations in the final histogram mass spectrum. Known mass analysers using time-to-digital converter detector systems therefore suffer from the following problems: have a relatively limited dynamic range for both quantitative and qualitative applications.

In contrast to the limitations of time-to-digital converter systems, multiple ion arrival events can be accurately recorded using an analog-to-digital converter system. The analog-to-digital converter system may record the signal strength of each clock cycle.

Known analog-to-digital recorders may digitize a signal at a rate of, for example, 2GHz while recording the strength of the signal as a digital value of up to eight bits. This corresponds to intensity values of 0-255 at each time digitization point. Analog-to-digital converters that can record digital intensity values in as many as 10 bits are also known, but such analog-to-digital converters tend to have limited spectral repetition rates.

The analog-to-digital converter produces a continuous intensity profile as a function of time corresponding to the signal output by the electron multiplier. The time-of-flight spectra from multiple acquisitions may then be summed together to produce a final mass spectrum.

One advantageous feature of the analog-to-digital converter system is: the analog to digital converter system may output intensity values and may therefore record multiple simultaneous ion arrival events by outputting increased intensity values. In contrast, time-to-digital converter systems are unable to distinguish between one or more ions arriving at the ion detector at substantially the same time.

The analog-to-digital converter is not subject to dead time effects that may be associated with time-to-digital converters that use detection thresholds. However, analog-to-digital converters suffer from the following problems: the analog width of the signal due to each ion arrival is added to the width of the ion arrival envelope. Thus, the mass resolution of the final sum or histogram mass spectrum may be reduced compared to a comparable mass spectrum produced using a time-to-digital converter based system.

Analog-to-digital converters also suffer from the following problems: any electronic noise will also be digitized and will appear in each time-of-flight spectrum for each acquisition. This noise will then be summed and will be present in the final mass spectrum or histogram mass spectrum. Consequently, weaker ion signals may be masked, which may result in poor detection limits compared to those achievable using time-to-digital converter based systems.

Disclosure of Invention

It is desirable to provide an improved mass spectrometer and method of mass spectrometry.

According to an aspect of the present invention, there is provided a method of mass spectrometry comprising:

digitizing a first signal output from the ion detector to produce a first digitized signal;

determining or obtaining a second differential or a second difference of the first digitized signal;

determining the arrival time T of one or more first ions from the second differential or second differential of the first digitised signal₁；

Determining the intensity I of one or more first ions₁；

Digitizing a second signal output from the ion detector to produce a second digitized signal;

determining or obtaining a second differential or a second difference of the second digitized signal;

determining the arrival time T of one or more second ions from the second differential or second difference of the second digitised signal₂；

Determining the intensity I of one or more second ions₂(ii) a And is

Determining a determined arrival time T of one or more second ions₂Determined arrival time T of whether one or more first ions fall₁A time period, time window or memory array cell into which the determined arrival time T of one or more second ions, if determined₂Determined arrival time T of one or more first ions falling therein₁Within a time period, time window, or memory array cell, the method further comprises: (i) determining T of one or more first ions₁And T of one or more second ions₂The average arrival time T'; and/or (ii) determining the I of one or more first ions₁And I of one or more second ions₂The combined strength I' of (1).

The step of determining or obtaining a second order differential of the first digitized signal and/or the second digitized signal is highly preferred but not essential to the invention.

The first and/or second signal preferably comprises an output signal, a voltage signal, an ion current, a voltage pulse or an electronic current pulse.

According to the preferred embodiment, the average arrival time T' follows the following relationship:

the combined intensity I' preferably follows the following relationship:

I′＝I₁+I₂

the method preferably further comprises replacing the determined arrival time T of the one or more first ions with the average arrival time T' and the combined intensity I₁And determining the intensity I₁And replacing the determined arrival time T of one or more second ions₂And determining the intensity I₂。

The time period, time window or memory array cell preferably has a width, wherein the width preferably falls within a range selected from the following ranges: (i) <1 ps; (ii)1-10 ps; (iii)10-100 ps; (iv) 100-; (v)200-300 ps; (vi)300-400 ps; (vii)400-500 ps; (viii)500-600 ps; (ix)600-700 ps; (x)700-800 ps; (xi) 800-; (xii) 900-; (xiii)1-2 ns; (xiv)2-3 ns; (xv)3-4 ns; (xvi)4-5 ns; (xvii)5-6 ns; (xviii)6-7 ns; (xix)7-8 ns; (xx)8-9 ns; (xxi)9-10 ns; (xxii)10-100 ns; (xxiii)100-500 ns; (xxiv)500- > 1000 ns; (xxv)1-10 mus; (xxvi)10-100 mus; (xxvii) 100-; (xxviii) Is more than 500 mu s.

The method preferably further comprises obtaining the first signal and/or the second signal over an acquisition time period, wherein the length of the acquisition time period is preferably selected from: (i) <1 μ s; (ii)1-10 mus; (iii)10-20 mus; (iv)20-30 mus; (v)30-40 mu s; (vi)40-50 mus; (vii)50-60 mu s; (viii)60-70 mus; (ix)70-80 mus; (x)80-90 mus; (xi)90-100 mus; (xii) 100-; (xiii) 110-; (xiv) 120-; (xv) 130-; (xvi) 140-; (xvii) 150-; (xviii) 160-; (xix) 170-; (xx) 180-; (xxi) 190-; (xxii) 200-; (xxiii) 250-; (xxiv) 300-; (xxv) 350-; (xxvi) 450-; (xxvii) 500-; and (xxviii) >1 ms.

The method preferably further comprises subdividing the acquisition time period into n time periods, time windows or memory array units, wherein n is preferably selected from: (i) < 100; (ii) 100-; (iii) 1000-; (iv)10,000-100,000; (v)100,000-200,000; (vi)200,000-300,000; (vii)300,000-400,000; (viii)400,000-500,000; (ix)500,000-600,000; (x)600,000-700,000; (xi)700,000-800,000; (xii)800,000-900,000; (xiii)900,000-; and (xiv) >1,000,000.

Each time period, time window or memory array cell preferably has substantially the same length, width or duration.

The method preferably further comprises digitising the first signal and/or the second signal using an analogue to digital converter or a transient recorder. The analog to digital converter or transient recorder preferably comprises an n-bit analog to digital converter or transient recorder, wherein n preferably comprises 8, 10, 12, 14 or 16.

The analog-to-digital converter or transient recorder preferably has a sampling or acquisition rate selected from the following: (i) <1 GHz; (ii)1-2 GHz; (iii)2-3 GHz; (iv)3-4 GHz; (v)4-5 GHz; (vi)5-6 GHz; (vii)6-7 GHz; (viii)7-8 GHz; (ix)8-9 GHz; (x)9-10 GHz; and (xi) >10 GHz.

According to one embodiment, the analog-to-digital converter or transient recorder has a substantially uniform digitization rate. According to an alternative embodiment, the analog-to-digital converter or the transient recorder may have a substantially non-uniform digitization rate.

The method preferably further comprises subtracting a constant or constant value from the first digitised signal and/or the second digitised signal. After subtracting the constant or constant value from the first digitized signal, if a portion of the first digitized signal falls below zero, the method preferably further comprises resetting the portion of the first digitized signal to zero.

After subtracting the constant or constant value from the second digitized signal, if a portion of the second digitized signal falls below zero, the method preferably further comprises resetting the portion of the second digitized signal to zero.

According to this preferred embodiment, the method further comprises smoothing the first digitized signal and/or the second digitized signal. According to one embodiment, the first digitized signal and/or the second digitized signal may be smoothed using a moving average, boxcar integrator (boxcar integrator), Savitsky Golay, or Hites Biemann algorithm.

Determining the arrival time of one or more first ions from the second differential of the first digitised signalT₁Preferably comprises determining one or more zero crossings of the second order differential of the first digitised signal.

The method preferably further comprises comparing the start time T of the ion arrival event_{1 start of}A digitization interval is determined or set corresponding to a time immediately before or after the second order differential of the first digitized signal falls below zero or other values.

The method preferably further comprises comparing the end time T of the ion arrival event_{1 end of}A digitization interval is determined or set corresponding to a time immediately before or after the time when the second order differential of the first digitized signal rises above zero or other value.

According to one embodiment, the method further comprises determining the intensity of one or more peaks present in the first digitised signal corresponding to one or more ion arrival events. The step of determining the intensity of one or more peaks present in the first digitised signal preferably comprises determining the mean time from the start T_{1 start of}And/or by an end time T_{1 end of}The area of one or more peaks defined to be present in the first digitized signal.

According to one embodiment, the method further comprises determining moments of one or more peaks present in the first digitised signal corresponding to the one or more ion arrival events. The step of determining the moment of one or more peaks present in the first digitised signal corresponding to one or more ion arrival events preferably comprises determining the time T from the start_{1 start of}And/or by an end time T_{1 end of}The moment of the defined peak.

The method preferably further comprises determining the centroid time of one or more peaks present in the first digitised signal corresponding to one or more ion arrival events.

According to one embodiment, the method further comprises determining an average or representative time of one or more peaks present in the first digitised signal corresponding to the one or more ion arrival events.

Determining the arrival time T of one or more second ions from the second derivative of the second digitised signal₂Preferably comprises determining one or more zero crossings of the second order differential of the second digitised signal.

According to one embodiment, the method further comprises timing the start of the ion arrival event T_{2 start of}A digitization interval is determined or set corresponding to a time immediately before or after the second derivative of the second digitized signal falls below zero or other value.

The method preferably further comprises comparing the end time T of the ion arrival event_{2 end of}A digitization interval is determined or set corresponding to a time immediately before or after the second order differential of the second digitized signal rises above zero or other value.

The method preferably further comprises determining the intensity of one or more peaks present in the second digitised signal corresponding to one or more ion arrival events. The step of determining the intensity of one or more peaks present in the second digitised signal preferably comprises determining the mean time from the start T_{2 start of}And/or by an end time T_{2 end of}The area of one or more peaks defined to be present in the second digitized signal.

According to this preferred embodiment, the method further comprises determining the moment of one or more peaks present in the second digitised signal corresponding to one or more ion arrival events. The step of determining the moment of one or more peaks present in the second digitised signal corresponding to one or more ion arrival events preferably comprises determining the time T from the start_{2 start of}And/or by an end time T_{2 end of}The moment of the defined peak.

The method preferably further comprises determining the centroid time of one or more peaks present in the second digitised signal corresponding to one or more ion arrival events.

According to one embodiment, the method preferably further comprises determining an average or representative time of one or more peaks present in the second digitised signal corresponding to one or more ion arrival events.

According to one embodiment, the method preferably further comprises:

digitizing one or more further signals output from the ion detector to produce one or more further digitized signals;

determining or obtaining a second differential or a second difference of one or more further digitised signals;

determining the arrival time T of one or more further ions from the second differential or second difference of one or more further digitised signals_n(ii) a And is

Determining the intensity I of one or more further ions_n。

The method preferably further comprises determining a determined arrival time T of one or more further ions_nDetermined arrival time T of one or more other ions₀A time period, time window or memory array cell into which the determined arrival time T of one or more additional ions, if determined_nDetermined arrival time T of one or more other ions falling therein₀Within a time period, time window, or memory array cell, the method further comprises: (i) determining T of one or more additional ions_nAnd T of one or more other ions₀Average arrival time T of_n'; and/or (ii) determining the I of one or more further ions_nAnd I of one or more other ions₀Combined strength of I_n’。

Mean time of arrival T_n' preferably follows the following relationship:

combined strength I_n' preferably follows the following relationship:

I_n′＝I_n+I₀

the method preferably further comprises using the average time of arrival T_n' and Combined Strength I_n' substitution of one or more additional ions for a determined arrival time T_nAnd determining the intensity I_nAnd replacing the determined arrival time T of one or more other ions₀And determining the intensity I₀。

According to one embodiment, the step of digitizing one or more further signals preferably comprises digitizing at least 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000 or 10000 signals from the ion detector. Each signal preferably corresponds to a separate experimental run or acquisition.

The method preferably further comprises storing the determined or average time and/or intensity of one or more peaks present in the digitised signal corresponding to one or more ion arrival events.

According to one embodiment, the method preferably further comprises subtracting a constant or constant value from at least some or each of the one or more further digitised signals. After subtracting the constant or constant value from the one or more further digitised signals, if a portion of at least some or each of the one or more further digitised signals falls below zero, the method preferably further comprises resetting the portion of the one or more further digitised signals to zero.

According to one embodiment, the method preferably further comprises smoothing the one or more further digitized signals. One or more of the further digitised signals may be smoothed using a moving average, boxcar integrator, Savitsky Golay or Hites Biemann algorithm.

The step of determining the time of arrival of one or more further ions from the second derivative of each of said one or more further digitised signals preferably comprises determining one or more zero crossings of each second derivative of one or more further digitised signals. The method preferably further comprises comparing the start time T of the ion arrival event_{n start}A digitization interval is determined or set to correspond to a time immediately before or after the second derivative of one or more additional digitized signals falls below zero or other values.

According to one embodiment, the method preferably further comprises determining or setting an end time Tn end of the ion arrival event to correspond to a digitization interval immediately before or after the time at which the second differential of one or more further digitized signals rises above zero or other value.

The step of determining the intensity of one or more further digitised signals relating to an ion arrival event preferably comprises determining the mean time from onset T_{n start}And/or an end time T_{n is over}The area of the defined output signal peak, voltage signal peak, ion current peak, or voltage pulse.

The method preferably further comprises determining the moment of one or more further digitised signals relating to the ion arrival event. According to one embodiment, ion arrival is determinedThe step of determining the moment of one or more further digitised signals relating to the article comprises determining a start time T_{n start}And/or an end time T_{n is over}A defined output signal peak, voltage signal peak, ion current peak, or moment of a voltage pulse.

The method preferably further comprises determining the centroid time of one or more further digitised signals relating to the ion arrival event.

According to one embodiment, the method preferably further comprises determining an average or representative time of one or more further digitised signals relating to the ion arrival event.

The method preferably further comprises storing an average or representative time and/or intensity of one or more further digitised signals relating to the ion arrival event.

According to one embodiment, the method preferably further comprises combining data relating to time and intensity of peaks relating to ion arrival events. The data relating to the time and intensity of the peak relating to the ion arrival event may be combined using a moving average integrator algorithm, a boxcar integrator algorithm, a Savitsky Golay algorithm, or a Hites Biemann algorithm.

According to this preferred embodiment, a continuous time spectrum or mass spectrum is preferably provided.

The method preferably further comprises determining or obtaining a second order differential or second order difference of the continuous time spectrum or mass spectrum. The method preferably further comprises determining the arrival time or mass to charge ratio of one or more ions, peaks or mass peaks from the second differential or second difference of the continuous time spectrum or mass spectrum.

The step of determining the time of arrival or mass to charge ratio of one or more ions, peaks or mass peaks from the second order differential of the continuous time spectrum or mass spectrum preferably comprises determining one or more zero crossings of the second order differential of the continuous time spectrum or mass spectrum.

The method preferably further comprises combining the peak or massStarting point M of peak_{Start of}Is determined or set to correspond to a step interval immediately before or after the point in time when the second derivative of the continuous-time or mass spectrum falls below zero or other value.

The method preferably further comprises locating the end point M of a peak or mass peak_{End up}Is determined or set to correspond to a step interval immediately before or after the point in time when the second order differential of the continuous time spectrum or mass spectrum rises above zero or other value.

According to this preferred embodiment, the method further comprises determining the intensity of the peak or mass peak from the continuous time spectrum or mass spectrum. The step of determining the intensity of a peak or mass peak from a continuous time spectrum or mass spectrum preferably comprises determining the intensity of the peak or mass peak from the starting point M_{Start of}And/or an end point M_{End up}The area of the defined peak or mass peak.

The method preferably further comprises determining the moment of the peak or mass peak from the continuous time spectrum or mass spectrum. The step of determining the moment of the peak or mass peak from the continuous time spectrum or mass spectrum preferably comprises determining the moment of the peak or mass peak from the starting point M_{Start of}And/or an end point M_{End up}The moment of a defined peak or mass peak.

The method preferably further comprises determining the centroid time or mass of a peak or mass peak from the continuous time spectrum or mass spectrum.

According to this preferred embodiment, the method further comprises determining an average or representative time or mass of a peak or mass peak from the continuous time spectrum or mass spectrum.

The method preferably further comprises converting the time data into mass or mass to charge ratio data.

The method preferably further comprises displaying or outputting the mass spectrum. The mass spectrum preferably comprises a plurality of mass spectrum data points, wherein each data point is considered to represent an ion, and wherein each data point comprises an intensity value and a mass or mass-to-charge ratio value.

According to a preferred embodiment, the ion detector comprises a microchannel plate, a photomultiplier, or an electron multiplier device.

The ion detector preferably further comprises a current to voltage converter or amplifier which generates a voltage pulse in response to one or more ions reaching the ion detector.

The method preferably further comprises providing a mass analyser. The mass analyser preferably comprises: (i) a time-of-flight ("TOF") mass analyzer; (ii) an orthogonal acceleration time of flight ("oaTOF") mass analyzer; or (iii) an axially accelerated time-of-flight mass analyser. Alternatively, the mass analyser may be selected from: (i) a magnetic sector mass spectrometer; (ii) paul or 3D quadrupole mass analyser; (iii) a 2D or linear quadrupole mass analyzer; (iv) a Penning trap mass analyzer; (v) an ion trap mass analyser; and (vi) a quadrupole mass analyzer.

According to another aspect of the present invention, there is provided an apparatus comprising:

means arranged to digitise a first signal output from the ion detector to produce a first digitised signal;

means arranged to determine or obtain a second differential or a second difference of the first digitised signal;

is arranged to determine the arrival time T of one or more first ions from the second differential or difference of the first digitised signal₁The apparatus of (1);

arranged to determine the intensity I of one or more first ions₁The apparatus of (1);

means arranged to digitise a second signal output from the ion detector to produce a second digitised signal;

means arranged to determine or obtain a second differential or a second difference of the second digitised signal;

is arranged to determine the arrival time T of one or more second ions from the second differential or second order difference of the second digitised signal₂The apparatus of (1);

arranged to determine the intensity I of one or more second ions₂The apparatus of (1); and

arranged to determine a determined arrival time T of one or more second ions₂Determined arrival time T of whether one or more first ions fall₁Time period, time window or arrangement within a memory array cell into which the second ion or ions fall, if the determined arrival time T of the second ion or ions is determined₂Determined arrival time T of one or more first ions falling therein₁Within the time period, time window, or memory array cell that falls, then the device further: (i) determining T of one or more first ions₁And T of one or more second ions₂The average arrival time T'; and/or (ii) determining the I of one or more first ions₁And I of one or more second ions₂The combined strength I' of (1). Determining or obtaining the second order differential of the first digitized signal and/or the second digitized signal is highly preferred, but not essential to the invention.

The average arrival time T' preferably follows the following relationship:

the combined intensity I' preferably follows the following relationship:

I′＝I₁+I₂

the apparatus preferably further comprises a determined arrival time T arranged to replace one or more first ions with the average arrival time T' and the combined intensity I₁And determining the intensity I₁And replacing the determined arrival time T of one or more second ions₂And determining the intensity I₂The apparatus of (1).

The apparatus preferably further comprises an analog-to-digital converter or transient recorder to digitize the first signal and/or the second signal. The analog to digital converter or transient recorder preferably comprises an n-bit analog to digital converter or transient recorder, where n comprises 8, 10, 12, 14 or 16.

The analog-to-digital converter or transient recorder preferably has a substantially uniform digitization rate. Alternatively, the analog-to-digital converter or the transient recorder may have a substantially non-uniform digitization rate.

According to another aspect of the present invention there is provided a mass spectrometer comprising an apparatus as described above.

According to one embodiment, the mass spectrometer further comprises an ion source. The ion source is preferably selected from: (i) an electrospray ionization ("ESI") ion source; (ii) an atmospheric pressure photoionization ("APPI") ion source; (iii) an atmospheric pressure chemical ionization ("APCI") ion source; (iv) a matrix-assisted laser desorption ionization ("MALDI") ion source; (v) a laser desorption ionization ("LDI") ion source; (vi) an atmospheric pressure ionization ("API") ion source; (vii) a desorption ionization on silicon ("DIOS") ion source; (viii) an electron impact ("EI") ion source; (ix) a chemical ionization ("CI") ion source; (x) A field ionization ("FI") ion source; (xi) A field desorption ("FD") ion source; (xii) An inductively coupled plasma ("ICP") ion source; (xiii) A fast atom bombardment ("FAB") ion source; (xiv) A liquid secondary ion mass spectroscopy ("LSIMS") ion source; (xv) A desorption electrospray ionization ("DESI") ion source; (xvi) A source of nickel-63 radioactive ions; (xvii) An atmospheric pressure matrix-assisted laser desorption ionization ion source; and (xviii) a thermal spray ion source.

The mass spectrometer may comprise a continuous or pulsed ion source.

The mass spectrometer preferably further comprises a mass analyser. The mass analyser preferably comprises: (i) a time-of-flight ("TOF") mass analyzer; (ii) an orthogonal acceleration time of flight ("oaTOF") mass analyzer; or (iii) an axially accelerated time-of-flight mass analyser. Alternatively, the mass analyser may be selected from: (i) a magnetic sector mass spectrometer; (ii) paul or 3D quadrupole mass analyser; (iii) a 2D or linear quadrupole mass analyzer; (iv) a Penning trap mass analyzer; (v) an ion trap mass analyser; and (vi) a quadrupole mass analyzer.

The mass spectrometer preferably further comprises a collision, fragmentation or reaction device. The collision, fragmentation or reaction means is preferably arranged to fragment the ions by collision induced dissociation ("CID"). Alternatively, the collision, lysis or reaction means may be selected from: (i) a surface induced dissociation ("SID") cleavage apparatus; (ii) an electron transfer dissociation cleavage device; (iii) an electron capture dissociation lysis device; (iv) electron collision or impact dissociation cracking device; (v) a light induced dissociation ("PID") lysis device; (vi) a laser induced dissociation cracking device; (vii) an infrared radiation induced dissociation device; (viii) an ultraviolet radiation induced dissociation device; (ix) a nozzle-dispenser interface cracking unit; (x) An endogenous lysis device; (xi) An ion source collision induced dissociation cracking device; (xii) A thermal or temperature source cracking unit; (xiii) An electric field induced cracking device; (xiv) A magnetic field induced lysis device; (xv) An enzymatic digestion or degradation cleavage unit; (xvi) An ion-ion reaction cracking device; (xvii) An ion-molecule reaction cracking device; (xviii) An ion-atom reaction cracking device; (xix) An ion-metastable ion reaction cracking device; (xx) An ion-metastable molecule reaction cracking device; (xxi) An ion-metastable atom reaction cracking device; (xxii) Ion-ion reaction means for reacting ions to form adduct or product ions; (xxiii) Ion-molecule reaction means for reacting the ions to form adduct or product ions; (xxiv) Ion-atom reaction means for reacting the ions to form adduct or product ions; (xxv) Ion-metastable ion reaction means for reacting ions to form adduct or product ions; (xxvi) Ion-metastable molecule reaction means for reacting the ions to form adduct or product ions; and (xxvii) an ion-metastable atom reaction device for reacting ions to form adduct or product ions.

According to another aspect of the present invention, there is provided a method of mass spectrometry comprising:

digitizing a first signal output from the ion detector;

determining the mass or mass-to-charge ratio m of one or more first ions from the second differential or second difference of the first digitised signal₁；

Determining the intensity I of one or more first ions₁；

Digitizing a second signal output from the ion detector;

determining the mass or mass-to-charge ratio m of one or more second ions from the second differential or second order difference of the second digitised signal₂；

Determining the intensity I of one or more second ions₂(ii) a And is

Determining a determined mass or mass to charge ratio m of one or more second ions₂Whether or not to fall within a determined mass or mass to charge ratio m of one or more first ions₁Within a mass window or predetermined memory location, which fallsIf the determined mass or mass to charge ratio m of one or more second ions is determined₂Determined mass or mass to charge ratio m falling into one or more first ions₁Within the mass window or predetermined memory location, the method further comprises: (i) determining m of one or more first ions₁And m of one or more second ions₂M' of the mass or mass to charge ratio; and/or (ii) determining the I of one or more first ions₁And I of one or more second ions₂The combined strength I' of (1). The step of determining or obtaining a second differential of the first digitized signal and/or the second digitized signal is highly preferred but not essential to the invention.

The average mass or mass to charge ratio m' preferably follows the relationship:

the combined intensity I' preferably follows the following relationship:

I′＝I₁+I₂

the method preferably further comprises replacing the determined mass or mass to charge ratio m of the one or more first ions with the average mass or mass to charge ratio m' and the combined intensity I₁And determining the intensity I₁And replacing the determined mass or mass to charge ratio m of one or more second ions₂And determining the intensity I₂。

means arranged to digitise a first signal output from the ion detector;

arranged to determine the mass or mass-to-charge ratio m of one or more first ions from the second differential or second differential of the first digitised signal₁The apparatus of (1);

means arranged to digitise a second signal output from the ion detector;

is arranged to determine the mass or mass-to-charge ratio m of one or more second ions from the second differential or second order difference of the second digitised signal₂The apparatus of (1);

arranged to determine a determined mass or mass to charge ratio m of one or more second ions₂Whether or not to fall within a determined mass or mass to charge ratio m of one or more first ions₁Means falling within the mass window or predetermined memory location, wherein the determined mass or mass to charge ratio m of one or more second ions if determined₂Determined mass or mass to charge ratio m falling into one or more first ions₁Within the mass window or predetermined memory location, the device further: (i) determining m of one or more first ions₁And m of one or more second ions₂M' of the mass or mass to charge ratio; and/or (ii) determiningI of one or more first ions₁And I of one or more second ions₂The combined strength I' of (1).

Determining or obtaining the second order differential of the first digitized signal and/or the second digitized signal is highly preferred, but not essential to the invention.

the combined intensity I' preferably follows the following relationship:

I′＝I₁+I₂

the apparatus preferably further comprises a determined mass or mass to charge ratio m arranged to replace one or more first ions with an average mass or mass to charge ratio m' and a combined intensity I₁And determining the intensity I₁And replacing the determined mass or mass to charge ratio m of one or more second ions₂And determining the intensity I₂The apparatus of (1).

The apparatus preferably further comprises an analog-to-digital converter or transient recorder to digitize the first signal and/or the second signal. The analog to digital converter or transient recorder preferably comprises an n-bit analog to digital converter or transient recorder, where n comprises 8, 10, 12, 14 or 16. The analog-to-digital converter or transient recorder preferably has a sampling or acquisition rate selected from the following: (i) <1 GHz; (ii)1-2 GHz; (iii)2-3 GHz; (iv)3-4 GHz; (v)4-5 GHz; (vi)5-6 GHz; (vii)6-7 GHz; (viii)7-8 GHz; (ix)8-9 GHz; (x)9-10 GHz; and (xi) >10 GHz.

The mass spectrometer preferably comprises an ion source. The ion source is preferably selected from: (i) an electrospray ionization ("ESI") ion source; (ii) an atmospheric pressure photoionization ("APPI") ion source; (iii) an atmospheric pressure chemical ionization ("APCI") ion source; (iv) a matrix-assisted laser desorption ionization ("MALDI") ion source; (v) a laser desorption ionization ("LDI") ion source; (vi) an atmospheric pressure ionization ("API") ion source; (vii) a desorption ionization on silicon ("DIOS") ion source; (viii) an electron impact ("EI") ion source; (ix) a chemical ionization ("CI") ion source; (x) A field ionization ("FI") ion source; (xi) A field desorption ("FD") ion source; (xii) An inductively coupled plasma ("ICP") ion source; (xiii) A fast atom bombardment ("FAB") ion source; (xiv) A liquid secondary ion mass spectroscopy ("LSIMS") ion source; (xv) A desorption electrospray ionization ("DESI") ion source; (xvi) A source of nickel-63 radioactive ions; (xvii) An atmospheric pressure matrix-assisted laser desorption ionization ion source; and (xviii) a thermal spray ion source.

The mass spectrometer preferably comprises a continuous or pulsed ion source.

According to one embodiment, the mass spectrometer preferably further comprises a collision, fragmentation or reaction device. The collision, fragmentation or reaction means is preferably arranged to fragment the ions by collision induced dissociation ("CID"). Alternatively, the collision, lysis or reaction means may be selected from: (i) a surface induced dissociation ("SID") cleavage apparatus; (ii) an electron transfer dissociation cleavage device; (iii) an electron capture dissociation lysis device; (iv) electron collision or impact dissociation cracking device; (v) a light induced dissociation ("PID") lysis device; (vi) a laser induced dissociation cracking device; (vii) an infrared radiation induced dissociation device; (viii) an ultraviolet radiation induced dissociation device; (ix) a nozzle-dispenser interface cracking unit; (x) An endogenous lysis device; (xi) An ion source collision induced dissociation cracking device; (xii) A thermal or temperature source cracking unit; (xiii) An electric field induced cracking device; (xiv) A magnetic field induced lysis device; (xv) An enzymatic digestion or degradation cleavage unit; (xvi) An ion-ion reaction cracking device; (xvii) An ion-molecule reaction cracking device; (xviii) An ion-atom reaction cracking device; (xix) An ion-metastable ion reaction cracking device; (xx) An ion-metastable molecule reaction cracking device; (xxi) An ion-metastable atom reaction cracking device; (xxii) Ion-ion reaction means for reacting ions to form adduct or product ions; (xxiii) Ion-molecule reaction means for reacting the ions to form adduct or product ions; (xxiv) Ion-atom reaction means for reacting the ions to form adduct or product ions; (xxv) Ion-metastable ion reaction means for reacting ions to form adduct or product ions; (xxvi) Ion-metastable molecule reaction means for reacting the ions to form adduct or product ions; and (xxvii) an ion-metastable atom reaction device for reacting ions to form adduct or product ions.

determining the arrival time T of one or more first ions₁；

Determining the intensity I of one or more first ions₁；

determining the arrival time T of one or more second ions₂；

Determining the intensity I of one or more second ions₂(ii) a And is

arranged to determine the arrival time T of one or more first ions₁The apparatus of (1);

arranged to determine the intensity of one or more first ionsI₁The apparatus of (1);

arranged to determine the arrival time T of one or more second ions₂The apparatus of (1);

arranged to determine a determined arrival time T of one or more second ions₂Determined arrival time T of whether one or more first ions fall₁Time period, time window or arrangement within a memory array cell into which the second ion or ions fall, if the determined arrival time T of the second ion or ions is determined₂Determined arrival time T of one or more first ions falling therein₁Within the time period, time window, or memory array cell that falls, then the device further: (i) determining T of one or more first ions₁And T of one or more second ions₂The average arrival time T'; and/or (ii) determining the I of one or more first ions₁And I of one or more second ions₂The combined strength I' of (1).

digitizing a first signal output from the ion detector;

determining the mass or mass to charge ratio m of one or more first ions₁；

Determining the intensity I of one or more first ions₁；

Digitizing a second signal output from the ion detector;

determining the mass or mass to charge ratio m of one or more second ions₂；

Determine oneIntensity I of one or more second ions₂(ii) a And is

Determining a determined mass or mass to charge ratio m of one or more second ions₂Whether or not to fall within a determined mass or mass to charge ratio m of one or more first ions₁Falls within a mass window or predetermined memory location, wherein the determined mass or mass to charge ratio m of one or more second ions, if determined₂Determined mass or mass to charge ratio m falling into one or more first ions₁Within the mass window or predetermined memory location, the method further comprises: (i) determining m of one or more first ions₁And m of one or more second ions₂M' of the mass or mass to charge ratio; and/or (ii) determining the I of one or more first ions₁And I of one or more second ions₂The combined strength I' of (1).

means arranged to digitise a first signal output from the ion detector;

arranged to determine the mass or mass-to-charge ratio m of one or more first ions₁The apparatus of (1);

means arranged to digitise a second signal output from the ion detector;

arranged to determine the mass or mass-to-charge ratio m of one or more second ions₂The apparatus of (1);

arranged to determine a determined mass or mass to charge ratio m of one or more second ions₂Whether or not to fall within a determined mass or mass to charge ratio m of one or more first ions₁Falling within a mass window or predetermined memory locationApparatus wherein if a determined mass or mass to charge ratio m of one or more second ions is determined₂Determined mass or mass to charge ratio m falling into one or more first ions₁Within the mass window or predetermined memory location, the device further: (i) determining m of one or more first ions₁And m of one or more second ions₂M' of the mass or mass to charge ratio; and/or (ii) determining the I of one or more first ions₁And I of one or more second ions₂The combined strength I' of (1).

According to a preferred embodiment, a plurality of time-of-flight spectra are preferably acquired by a time-of-flight mass analyser, preferably comprising an ion detector incorporating an analogue to digital converter. The detected ion signal is preferably amplified and converted to a voltage signal. The voltage signal is then digitized, preferably using a fast analog-to-digital converter. The digitized signal is then preferably processed.

The start times of the discrete voltage peaks present in the digitised signal corresponding to the arrival of one or more ions at the ion detector are preferably determined. Similarly, the end time of each discrete voltage peak is also preferably determined. The intensity and moment of each discrete voltage peak is then preferably determined. The determined start time and/or end time of each voltage peak, the intensity of each voltage peak and the moment of each voltage peak are preferably used or stored for further processing.

Subsequently acquired data is then preferably processed in a similar manner. After multiple acquisitions are performed, the data from the multiple acquisitions are preferably combined, and a list of ion arrival times and corresponding intensity values associated with the ion arrival events is preferably formed, created or compiled. The time and corresponding intensity values from multiple acquisitions are then preferably integrated to form a coherent or continuum spectrum or mass spectrum.

Preferably the coherent or continuum or mass spectrum is further processed. The intensity and arrival time or mass to charge ratio of peaks or mass peaks present in a coherent or continuum or mass spectrum is preferably determined. A spectrum or mass spectrum is then preferably generated including the ion arrival time or ion mass or mass to charge ratio and the corresponding intensity values. According to this preferred embodiment, the time-of-flight data is preferably converted into mass spectral data.

According to this preferred embodiment, a second order differential of the ion or voltage signal, preferably output from the ion detector, is preferably determined. The start time of a voltage peak present in the ion or voltage signal is preferably determined as the time at which the second derivative of the digitised signal falls below zero. Similarly, the end time of the voltage peak is preferably determined as the time at which the second differential of the digitized signal rises above zero.

According to a less preferred embodiment, the start time of the voltage peak may be determined as the time at which the digitized signal rises above a predetermined threshold. Similarly, the end time of the voltage peak may be determined as the time at which the digitized signal subsequently falls below a predetermined threshold.

The intensity of the voltage peak is preferably determined from the sum of all digitized measurements defined by the determined start time of the voltage peak and ending with the determined end time of the voltage peak.

The moment of the voltage peak is preferably determined for all digitized measurements defined by the start time and the end time of the voltage peak from the sum of each digitized measurement and the product of that digitized measurement and the number of digitized time intervals between the voltage peak start time or the voltage peak end time.

Alternatively, the moment of the voltage peak may be determined from the sum of the voltage peak operating intensities when the peak intensities are progressively calculated from time interval to time interval by adding each successive digitized measurement between the voltage peak start time and the voltage peak end time.

The start time and/or end time of each voltage peak, the intensity of each voltage peak and the moment of each voltage peak obtained for each acquisition are preferably recorded and preferably used.

The start time and/or end time of a voltage peak, the intensity of the voltage peak and the moment of the voltage peak are preferably used to calculate a representative or average time-of-flight of one or more ions detected by the ion detector. The representative or average time of flight may then preferably be recorded or stored for further processing.

The representative or average time-of-flight of one or more ions may be determined by dividing the moment of the voltage peak by the intensity of the voltage peak to determine the centroid time of the voltage peak. Then, as the case may be, the centroid time of the voltage peak may be added to the start time of the voltage peak, or the end time of the voltage peak may be subtracted from the centroid time of the voltage peak. Advantageously, the representative or average time of flight may be calculated to a higher accuracy than the accuracy of the digitised time interval.

The representative or average time of flight and corresponding intensity values associated with each voltage peak obtained for each acquisition are preferably stored. The data from the multiple acquisitions are then preferably assembled or combined into a single data set comprising time and corresponding intensity values.

A single data set comprising representative or average time-of-flight and corresponding intensity values acquired over multiple acquisitions is then preferably processed so that the data is preferably integrated to form a single coherent or continuum mass spectrum. According to one embodiment, an integration algorithm may be used to integrate the time and intensity pairs. According to one embodiment, the data may be integrated by one or more passes of a boxcar integrator, a moving average algorithm, or other integration algorithm.

The resulting single coherent or continuum spectrum or mass spectrum preferably comprises a continuum of intensities at uniform or non-uniform time, mass or mass-to-charge ratio intervals. If a single coherent or continuum spectrum or mass spectrum includes continuum intensities at uniform time intervals, these time intervals may or may not correspond to simple fractions or integer multiples of the digitization time intervals of the analog-to-digital converter.

According to this preferred embodiment, the frequency of the intensity data intervals is preferably such that the number of intensity data intervals within a peak or mass peak is greater than four, more preferably greater than eight. According to one embodiment, the number of intensity data intervals within a peak or mass peak may be sixteen or more.

The resulting single coherent or continuum spectrum or mass spectrum may then be further processed such that the data or mass spectral data is preferably reduced to time-of-flight, mass or mass-to-charge ratio values and corresponding intensity values.

According to this preferred embodiment, a single coherent or continuum spectrum or mass spectrum is preferably processed in a similar manner to the way that the resulting voltage signal is preferably processed per acquisition to reduce the coherent or continuum spectrum or mass spectrum to a plurality of time-of-flight, mass or mass-to-charge ratio values and associated intensity values. A discrete mass spectrum may preferably be generated or output by converting time-of-flight data into mass spectral data.

According to this preferred embodiment, the start time or point of each peak, mass peak or data peak observed in the continuum or mass spectrum is preferably determined. Similarly, the end time or point of each peak, mass peak or data peak is also preferably determined. The intensity of each peak, mass peak or data peak is then preferably obtained. It is also preferred to obtain the moment for each peak, mass peak or data peak. The time of flight of each peak, mass peak or data peak is preferably obtained from the start time or point of the peak, mass peak or data peak and/or the end time or point of the peak, mass peak or data peak, the resultant moment of the peak, mass peak or data peak and the resultant intensity of the data peak.

The start time or point of a peak, mass peak, or data peak may be determined as the time at which the coherent or continuous spectrum or mass spectrum rises above a predetermined threshold. A subsequent end time or point of a peak, mass peak, or data peak may be determined as the time at which a coherent or continuous spectrum or mass spectrum falls below a predetermined threshold.

Alternatively, the start time or point of a peak, mass peak, or data peak may be determined as the time or point at which the second differential of a coherent or continuum spectrum or mass spectrum falls below zero or other values. Similarly, the end time or point of a peak, mass peak, or data peak may be determined as the time or point at which the second order differential of the coherent or continuum spectrum or mass spectrum later rises above zero or other value.

The composite intensity of a peak, mass peak, or data peak may be determined from the sum of the intensities of all the mass or data points bounded by the start time or point of the peak, mass peak, or data peak and the end time or point of the peak, mass peak, or data peak.

The resultant moment of each peak, mass peak or data peak is preferably determined for all mass or data points bounded by the start time or point and the end time or point of the mass peak or data peak, from the sum of the products of each mass or data point intensity and the mass peak or data peak time of flight and the time difference between the start time or point or the end time or point.

The time of flight of a peak, data, or mass peak can be determined by dividing the resultant moment of the peak, mass peak, or data peak by the resultant intensity of the peak, mass peak, or data peak to determine the centroid time of the peak, mass peak, or data peak. Then, as the case may be, the centroid time of a peak, mass peak or data peak is preferably added to the start time or point of the peak, mass peak or data peak, or the end time or point of the peak, mass peak or data peak is subtracted from the centroid time of the peak, mass peak or data peak. The time of flight of a peak, mass peak or data peak may be calculated to a higher precision than the precision of the digitised time interval and to a higher precision than the precision of each peak, mass peak or data peak.

The set of time of flight and corresponding intensity values for each peak, mass peak or data peak may then be converted into a set of mass or mass-to-charge ratio values and corresponding intensity values. Conversion of time-of-flight data to mass or mass-to-charge ratio data may be performed by converting the data using a relationship derived from a calibration process, as is well known in the art.

Drawings

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 shows a portion of an original unprocessed synthetic mass spectrum of polyethylene glycol acquired by ionizing a sample using a MALDI ion source and mass analyzing the resulting ions using an orthogonal acceleration time-of-flight mass analyzer;

FIG. 2 shows one spectrum acquired from a single experimental run and summed with other spectra to form the composite mass spectrum shown in FIG. 1;

FIG. 3 shows the spectrum shown in FIG. 2 after being processed to provide data in the form of mass-to-charge ratios and intensity pairs in accordance with a preferred embodiment;

FIG. 4 shows the result of summing or combining 48 individual processed time-of-flight mass spectra;

FIG. 5 shows the result of using a boxcar integration algorithm to integrate the data pairs shown in FIG. 4 to form a continuum mass spectrum;

FIG. 6 shows the second order differential of the continuum mass spectrum shown in FIG. 5; and

figure 7 shows the resulting mass peaks derived from the data shown in figure 4 by reducing the continuum mass spectrum shown in figure 5 to a discrete mass spectrum.

Detailed Description

According to a preferred embodiment, there is preferably provided a time-of-flight mass analyser of the type: which preferably includes a detector system incorporating an analog to digital converter rather than a conventional time to digital converter. The ions are preferably mass analysed by a time of flight mass analyser and preferably detected by an ion detector. The ion detector preferably includes a microchannel plate (MCP) electron multiplier assembly. A current-to-voltage converter or amplifier is preferably provided: which preferably generates a voltage pulse or signal in response to an electron pulse output from the microchannel plate ion detector. The voltage pulse or signal that arrives at the ion detector in response to a single ion preferably has a full width at half maximum of 1ns to 3 ns.

The voltage pulses or signals generated by the arrival of one or more ions at the ion detector of the time-of-flight mass analyser are preferably digitised using, for example, a fast 8-bit transient recorder or analogue to digital converter (ADC). The sampling rate of the transient recorder or analog-to-digital converter is preferably 1GHz or faster.

The voltage pulses or signals may be signal thresholded, with a constant or constant value preferably subtracted from each number of analog-to-digital converter outputs to remove most of any analog-to-digital converter noise. After subtracting the constant or constant value, the part of the signal is preferably reset to zero if the signal becomes negative.

Determining start and end times of voltage peaks

A smoothing algorithm, such as a moving average or boxcar integrator algorithm, is preferably applied to the spectrum output from the analog-to-digital converter. Alternatively, the Savitsky Golay algorithm, the Hites Biemann algorithm, or other types of smoothing algorithms may be applied to the data. For example, the average of the shifts made in a single pass over three windows at digitization intervals is given by:

s(i)＝m(i-1)+m(i)+m(i+1) (1)

where m (i) is the intensity value in bits recorded in the analog-to-digital converter time bin i and s (i) is the result of the smoothing process.

A multi-pass smoothing algorithm may be applied to the data.

After smoothing the raw time-of-flight ADC data, a second order differential of the preferably smoothed data is preferably obtained or determined to detect the presence of any ion arrival events or peaks.

The zero crossings of the second order differential are preferably determined and preferably used to indicate or determine the start time and end time of each observed voltage peak or ion signal peak. This peak localization method is particularly advantageous if the noise level is not constant over the entire time-of-flight spectrum or if the noise level fluctuates between individual time-of-flight spectra.

A simple differential calculation with a moving window of three digitization intervals will result in a first order differential D1(i) of the digitized signal, which can be represented by:

D1(i)＝s(i+1)-s(i-1) (2)

where s (i) is the result of any smoothing process entered for time bin i.

The differential calculation can then be repeated, preferably with three shifted windows of digitization intervals. Accordingly, a second order differential D2(i) of the first order differential D1(i) will be obtained. This can be represented by the following formula:

D2(i)＝D1(i+1)-D1(i-1) (3)

the second order differential can thus be represented by:

D2(i)＝s(i+2)-2.s(i)+s(i-2) (4)

this difference calculation can be performed with different moving window widths. The width of the difference window is preferably 33% to 100%, more preferably about 67%, of the full width at half maximum of the voltage pulse.

The second order differential D2(i) is preferably complete to locate or determine the start time and end time of the observed voltage peak. The start time t1 of the voltage peak may be taken as the digitization interval immediately after the second order differential falls below zero. The end time t2 of the voltage peak may be taken as the digitization interval immediately before the second order differential rises above zero. Alternatively, the start time t1 of the voltage peak may be taken as the digitization interval immediately before the second order differential falls below zero, and the end time t2 of the voltage peak may be taken as the digitization interval immediately after the second order differential rises above zero.

According to a less preferred embodiment, the voltage peak start time t1 may be derived from the digitisation time when the value m (i) of the analogue to digital converter output rises above a threshold level. Similarly, the voltage peak end time t2 may be derived from the digitisation time at which the value m (i) of the analogue to digital converter output falls below a threshold level.

Determining the intensity and moment of each voltage peak

Having determined the start time and end time of a voltage peak or ion signal peak, the intensity and moment of the voltage peak or ion signal peak, as defined by the start time and end time, is preferably determined.

The peak intensity of the voltage or ion signal preferably corresponds to the area of the peak or signal, and is preferably described by the following formula:

where I is the determined voltage peak intensity, m_iIs the intensity value in bits recorded in the analog-to-digital converter time bin i, t1 is the number of the analog-to-digital converter digitized time bin corresponding to the beginning of the voltage peak, and t2 is the number of the analog-to-digital converter digitized time bin corresponding to the end of the voltage peak.

Moment M relative to the beginning of the voltage peak₁Preferably described by the formula:

moment M relative to the end of the voltage peak₂Preferably described by the formula:

wherein:

δt＝t2-t1 (8)

of particular interest is the moment M relative to the end of the voltage peak₂And (4) calculating. Alternatively, M may be calculated using the following equation₂：

The above equation shows a form of computation that is fast to perform. It can be rewritten as follows:

wherein I_iIs the intensity calculated at each stage when equation (5) is performed.

The moment can thus be calculated when calculating the intensity. The moment is preferably obtained by summing the accumulations of the intensity at each stage when the intensity is calculated.

According to one embodiment, such computations may be performed very quickly using a Field Programmable Gate Array (FPGA) in which the computations of large data arrays may be performed in an essentially parallel manner.

The calculated intensity and moment values and the number of time bins corresponding to the start time and/or end time of the voltage peak or ion signal are preferably recorded for further processing.

Determining centroid time-of-flight values for each voltage peak

By dividing the moment of the voltage peak by the area or intensity of the voltage peak, the centroid time C of the voltage peak relative to the start of the peak can be calculated₁：

If the time bin recorded as the beginning of a voltage peak is t1, then the representative or average time t associated with the voltage peak is:

t＝t1+C₁ (12)

on the other hand, the centroid time C of the voltage peak relative to the end of the peak₂Can be calculated from the following formula:

if the time bin recorded as the end of the voltage peak is t2, then the representative or average time t associated with the voltage peak is:

t＝t2-C2 (14)

the accuracy of the calculated value of t depends on the accuracy of the division calculated in equation (11) or (13). The division calculation is slow compared to other calculations in the process, so the higher the required accuracy, the longer the required calculation time.

According to one embodiment, the start and end times t1, t2, the corresponding intensities I and the calculated moments M of each voltage peak in the spectrum are preferably recorded₁Or M₂. The corresponding ion arrival times may be calculated offline. This method allows t to be calculated to any required accuracy. Alternatively, the value of t may be calculated in real time.

Storing ion arrival times and corresponding intensity values at memory locations in an array

A single time-of-flight spectrum may include several voltage peaks resulting from multiple ions arriving at the detector. Each voltage peak is preferably analyzed and converted into a time value and a corresponding intensity value. The time and intensity value of each voltage peak is preferably stored in one of the memory locations in the array. The memory locations in the array preferably correspond to or relate to a predetermined time interval or sub-portion of the time-of-flight spectrum. For example, a time-of-flight spectrum may have a duration of 100 μ s, which may be subdivided into 500,000 equal time intervals in an array. Each time interval or sub-portion will have a width or duration of 200 ps.

Combining time and intensity values from multiple time-of-flight spectra

Subsequent time-of-flight spectra are preferably obtained and processed in a similar manner to that described above, i.e., the spectra are preferably analyzed and time and intensity values corresponding to ion arrival events are preferably determined. If the determined ion time of flight from the subsequent time of flight spectrum falls within a time interval, sub-section or memory array cell that already contains time and corresponding intensity values, then according to the preferred embodiment, the two data values are preferably combined to obtain a new single time value and corresponding intensity value. The new time-of-flight value t' is preferably calculated using a weighted average or centroid calculation:

wherein t is₁Is the time of flight, I, of the ion from the first time of flight spectrum₁Is a corresponding intensity value, and wherein t₂Is the time of flight, I, of the ion from the second time of flight spectrum₂Are the corresponding intensity values. t is t₁And t₂All falling within the same time interval, sub-portion or memory array cell.

The new intensity I' is preferably calculated by adding the two intensities:

I′＝I₁+I₂ (16)

the above process of combining data in a weighted manner for data falling within the same time interval, sub-portion or memory array cell is preferably repeated for a desired number of time-of-flight spectra. Upon completion of this processing, an ordered list of times and corresponding intensity values is preferably generated.

Further processing of the synthesis time and intensity data

The time and intensity pairs are then further processed by applying a smoothing function, according to one embodiment, to provide a continuum. The preferably smoothed data is then preferably subjected to peak detection and peak centroid calculation in a manner similar to that previously discussed for voltage peaks. Accordingly, a second order differential of the continuum is preferably obtained and the start and end times of the peaks are preferably determined. The intensity and centroid time of each peak is preferably determined. The width and increment used in the smoothing and double difference calculations may be independent of the digitization rate of the ADC.

According to this preferred embodiment, the intensity and time-of-flight values obtained from the plurality of spectra are preferably combined into a single composite list. The resultant data set is then preferably processed using, for example, a moving average or boxcar integrator algorithm. The moving window preferably has a time width w (t) and the time increment by which the moving window is stepped is preferably s (t). W (t) and s (t) may each be assigned values that are completely independent of each other and completely independent of the analog-to-digital converter digitization interval. W (t) and s (t) may each have a constant value, or may be a variable function of time.

According to the preferred embodiment, the width w (t) of the integration window is preferably 33% to 100% of the full width at half maximum of the mass peak, more preferably about 67%. The step interval s (t) is preferably such that the number of steps within a mass peak is at least four, or more preferably at least eight, and even more preferably sixteen or more.

The intensity data within each window is preferably summed and each intensity sum is preferably recorded along with the time interval corresponding to the step in which the summation occurred.

If n is the number of steps over a step interval S (t) of time T (n), the sum G (n) resulting from the simple moving average or boxcar integrator algorithm for the first pass is given by:

where T (n) is the time after n steps of the step interval S (t), I (t) is the intensity of the voltage peak recorded at the average or representative time of flight t, W (T) is the width of the integration window at time T (n), G (n) is the sum of the intensities of all voltage peaks within the integration window W (T) where the time of flight is centered at time T (n).

According to one embodiment, a multi-pass integration algorithm may be applied to the data. A smooth continuous composite data set is then preferably provided. The resulting continuous synthetic data set or continuous mass spectrum may then preferably be further analyzed.

Analytically synthesized continuous or mass spectra

The peak shape heart time and intensity calculated from the data, which represents the composite spectrum of all acquired data, are preferably stored.

According to this method, it is preferable to achieve data volume compression while maintaining the accuracy of each individual measurement, thereby reducing processing requirements.

According to this preferred embodiment, the intensity and the corresponding average or list of representative time-of-flight pairs are preferably converted into mass spectral data comprising mass or mass-to-charge ratio values and intensities, thereby preferably producing a mass spectrum.

According to this preferred embodiment, the second order differential of the smoothed continuum composite data set or continuum mass spectrum is preferably determined.

The zero crossings of the second order differential of the continuum mass spectrum are preferably determined. The zero crossings of the second order differential indicate the start and end times of a peak or mass peak in the synthetic continuous data set or mass spectrum.

The first and second order differentials may be determined by two successive differential calculations. For example, a differential calculation with a moving window of 3 step intervals will result in a first order differential H1(n) of the continuous data G, which can be represented by:

H1(n)＝G(n+1)-G(n-1) (18)

where G (n) is the final sum of the integration algorithm for one or more passes at step n.

If this simple difference calculation is repeated again with a moving window of 3 digitization intervals, this will result in a second order differential H2(n) of the first order differential H1 (n). This can be represented by the following formula:

H2(i)＝H1(i+1)-H1(i-1) (19)

the combination of the two difference calculations can be represented by:

H2(n)＝G(n+2)-2.G(n)+G(n-2) (20)

this difference calculation can be performed with different moving window widths. The width of the difference window is preferably 33% to 100%, more preferably about 67%, of the full width at half maximum of the mass peak.

The second order differential H2(n) is preferably used to locate the start and end times of peaks or mass peaks observed in a continuum or mass spectrum. The start time T1 of the peak or mass peak is preferably a step interval before the second order differential falls below zero. The end time T2 of the peak or mass peak is preferably a step interval after the second order differential rises above zero. Alternatively, the start time T1 of the peak or mass peak may be the step interval after the second differential falls below zero, and the end time T2 of the peak or mass peak may be the step interval before the second differential rises above zero.

According to another embodiment, the start time T1 of a peak or mass peak may be interpolated over a step interval before and after the second differential falls below zero, and the end time T2 of a peak or mass peak may be interpolated over a step interval before and after the second differential rises above zero.

According to a less preferred embodiment, the peak or mass peak start time T1 and the peak or mass peak end time T2 may be derived from the step time taken for the value of the integration process output G to rise above a threshold level and then fall below the threshold level.

After the start time and end time of a peak or mass peak are determined, the values corresponding to the intensities and moments of the peaks or mass peaks within the defined region are preferably determined. The intensity and moment of a peak or mass peak is preferably determined from the intensity and time of flight of the peak or mass peak defined by the peak or mass peak start time and the peak or mass peak end time.

The peak or mass peak intensity corresponds to the sum of intensity values defined by the peak or mass peak start time and the peak or mass peak end time, and can be described by the following equation:

wherein A is the peak or mass peak intensity, I_tIs the intensity of the peak or mass peak at time of flight T, T1 is the start time of the peak or mass peak, and T2 is the end time of the peak or mass peak.

The moment of each peak or mass peak is preferably determined from the sum of the moments of all peaks or mass peaks defined by the peak or mass peak start time and the peak or mass peak end time.

Moment B of a peak or mass peak relative to the start of the peak₁Preferably from the intensity and time difference of each peak or mass peak relative to the time of start of the peak or mass peak, and is preferably given by:

moment B relative to peak or mass peak end time₂Given by:

with calculation of the moment B relative to the start of the peak or mass peak₁By contrast, the moment B relative to the peak or mass peak end time is calculated₂No particular advantage is obtained.

The representative or average time Tpk associated with a peak or mass peak is given by:

the accuracy of the calculated value of Tpk depends on the accuracy of the division calculated in equation (24), and Tpk can be calculated to any desired accuracy.

Converting time-of-flight data to mass spectral data

The values Tpk and a for each peak or mass peak are preferably stored in a list in the computer memory. The peak or mass peak list may be assigned a mass or mass to charge ratio using the time of flight of the peak or mass peak and the relationship between time of flight and mass derived from the calibration process. Such calibration procedures are well known in the art.

The simplest form of the time-mass relationship for a time-of-flight mass spectrometer is given by:

M＝k.(t+t^*)² (25)

wherein t is^＊Is an instrument parameter equivalent to the time of flight offset, k is a constant, and M is the mass-to-charge ratio at time t.

More complex calibration algorithms can be applied to the data. For example, the calibration procedures disclosed in GB-2401721(Micromass) or GB-2405991(Micromass) may be used.

Alternative embodiments in which time-of-flight data is initially converted to mass spectral data

According to an alternative embodiment, the time-of-flight value associated with each voltage peak may be initially converted to mass or mass-to-charge ratio using a time-to-mass relationship as described previously in equation (25). The masses or mass-to-charge ratios and corresponding intensity values are preferably stored in memory locations in an array, which preferably correspond to or relate to predetermined intervals or sub-portions of the mass spectrum.

The integration process described above is then preferably applied to any mass data falling within the same mass interval, subsection or memory array cell of the mass spectrum. Thus forming a single composite mass spectrum rather than a list of time and intensity values that are converted to mass spectra at the final stage in the process.

The integration window w (m) and/or the step interval s (m) may each be set to a constant value or a function of mass. For example, the step interval function s (m) may be set to give a substantially constant number of steps within each mass spectral peak.

This method has several advantages over other known methods. The accuracy and precision of the measurement is preferably improved relative to other arrangements that may use simple measurements of the maxima or vertices of the signal. This is a result of using substantially the entire signal recorded within the measurement, rather than just measuring at or near the vertex. The preferred method also gives an accurate representation of the average arrival time when the ion signal is asymmetric due to the substantially simultaneous arrival of two or more ions. The signal maximum measurement will no longer reflect the average arrival time or relative strength of these signals.

The time value t associated with each detected ion signal can be calculated with a higher accuracy than the original accuracy imposed by the digitization rate of the analog-to-digital converter. For example, for a voltage peak full width at half maximum of 2.5ns and an analog-to-digital converter digitization rate of 2GHz, time-of-flight can typically be calculated to an accuracy of ± 125ps or higher.

According to this embodiment, the time data is preferably initially converted to mass or mass to charge ratio data. Then, a combination algorithm preferably operating on mass or mass to charge ratio data is preferably used.

According to this embodiment, the arrival time calculated for each ion signal is preferably initially squared. Thus, the value with which the ion arrives is now directly related to the mass or mass-to-charge ratio of the ion. The mass or mass-to-charge ratio value may also be multiplied by a factor to convert the mass or mass-to-charge ratio to a nominal mass.

The mass or mass-to-charge ratio values and areas (i.e. intensities) calculated for each ion signal are preferably stored in one of the memory locations in the array corresponding to a predetermined mass or mass-to-charge ratio interval which preferably subdivides the spectrum. For example, mass or mass to charge ratio values and corresponding areas may be stored in an array having a spacing of 1/256 mass units.

If the mass or mass to charge ratio value recorded for an ion signal in a subsequent data set falls within a predetermined mass or mass to charge ratio interval, sub-section or memory array element which already contains mass or mass to charge ratio values and corresponding intensity values, then the two data values are preferably combined to give a single mass or mass to charge ratio value and a single corresponding intensity value. The new mass or mass-to-charge ratio value m' is preferably calculated using a weighted average or centroid calculation:

wherein m is₁Is the ion mass or mass to charge ratio, I, from the first data set₁Is the corresponding intensity value, m₂Is the ion mass or mass to charge ratio, I, from the second data set₂Are the corresponding intensity values. m is₁And m₂All falling within the same mass or mass to charge ratio window, spacing, subdivision, or memory array cell.

The new intensity I' is preferably calculated by adding the two intensities:

I′＝I₁+I₂ (27)

the above process is preferably repeated for a desired number of time-of-flight spectra, preferably resulting in a final synthetic ordered list of mass or mass-to-charge ratio values and corresponding intensity values.

The resultant mass or mass-to-charge ratio data can then be further processed by applying a smoothing function to provide a continuum mass spectrum. Peak detection and peak centroid calculation is then preferably performed based on continuum mass spectrometry in a manner substantially as described above. Each detected and measured peak preferably corresponds to a respective mass peak. The widths and increments used in the smoothing and double difference calculations are preferably in units of mass or mass-to-charge ratios and are preferably independent of the digitization rate of the ADC.

The peak-shaped heart masses or mass-to-charge ratios and corresponding intensities of the mass peaks, which represent the composite spectra of all acquired data, are preferably stored.

According to this embodiment, each ion arrival time is converted directly to mass or mass-to-charge ratio after initial detection.

Background peak subtraction

According to one embodiment, the process of combining time or quality data falling within the same time or quality interval, subsection, or memory array cell may use up to three scan ranges and background factors. The first range (average) preferably defines the range of scans across the chromatographic peak that will be averaged together to form a representative spectrum of the compound of interest.

One or two other ranges (subtraction) may be used to define the range of the scan on each side of the peak, starting from the background of the chromatogram. These scans are preferably averaged together to form a representative background spectrum.

Finally, the background spectral intensity may be multiplied by a background factor (X), and then the averaged peak top spectrum may be subtracted by the product of the background spectral intensity and the background factor (X) to form a combined spectrum.

The combining process preferably has three stages. The first stage is to divide the mass scale and combine the spectra in the "average" and "subtraction" ranges, respectively, thereby forming a combined average spectrum and a combined subtraction spectrum. The second stage is to perform the subtraction and form a combined result spectrum. The third stage is to reform the mass scale.

In the first and third stages, the peak mass and intensity are preferably calculated based on the following formula:

MassCurr＝((MassCurr＊IntCurr)+(MassNew＊IntNew))/

(IntCurr+IntNew)

IntCurr＝IntCurr+IntNew

where masstcurr is the current adjusted mass, MassNew is the new mass, IntCurr is the current adjusted intensity, and IntNew is the new intensity.

According to the first stage, the mass range may for example be divided into mass windows of width 0.0625amu, preferably centred on the nominal mass. Thus, the mass range between 41.00 and 42.00 will be partitioned using the following boundaries:

40.96875 41.21875 41.46875 41.71875 41.96875

41.03125 41.28125 41.53125 41.78125 42.03125

41.09375 41.34375 41.59375 41.84375

41.15625 41.40625 41.65625 41.90625

all scans within the "average" range are used in turn, and each peak mass is then preferably assigned to one of these mass windows. If a peak or a combination of peaks already exists in a particular quality window, the quality (MassNew) and intensity (IntNew) values of that peak are preferably combined with the current value (MassCurr, IntCurr) to form a new current value.

For example, adding a peak of mass 44.5791, intensity 1671, to a mass window containing data with current mass 44.5635 and current intensity 1556 would initiate the merge as follows:

MassCurr＝((44.5635＊1556)+(44.5791＊1671))/

(1556+1671)

＝44.5716

IntCurr ＝1556+1671＝3227

after all peaks of all scans within the "average" range have been processed, the intensity in each window (IntCurr) is preferably divided by the total number of scans within the "average" range to form a combined average spectrum.

Then, the same processing is preferably performed using all scans in the "subtraction" range. The final intensity is preferably divided by the total number of scans in the "subtracted" range. If there are two "subtraction" ranges, then the final intensity is preferably divided by the total number of scans in the two ranges.

All intensity values are preferably multiplied by a magnification factor (X) to obtain a combined subtraction spectrum.

PREFERRED EMBODIMENTS

An important aspect of the preferred embodiment of the present invention is: the voltage peak time can be stored with significantly higher precision than that provided by the ADC digitization interval or a simple fraction of the ADC digitization interval.

According to one embodiment, the data may be processed to produce a final spectrum in which the number of step intervals within each mass spectral peak (ion arrival envelope) is substantially constant. It is known that for a time-of-flight spectrum recorded using a constant digitization interval (or which is constructed from many time-of-flight spectra with a constant bin width using histogram techniques), the number of points per mass peak (ion arrival envelope) increases with mass. This effect may complicate further processing and may lead to an unnecessary increase in the amount of data to be stored. According to this embodiment, there is no constraint on the choice of step interval, and the step interval function may be set to achieve a constant number of steps within each mass peak.

The following analysis illustrates one example of such a step interval function. The resolution R of an orthogonal acceleration time-of-flight mass spectrometer is approximately constant with mass-to-charge ratio, except at low mass-to-charge ratios:

where R is the mass resolution, t is the time of flight of the mass peak, and At is the width of the ion arrival envelope forming the mass peak.

With approximately constant resolution, the peak width is proportional to the time of flight t:

thus, in order to obtain an approximately constant number of steps within a mass peak, the step interval s (t) needs to be increased approximately proportional to the time of flight t.

For mass spectrometers where the relationship between resolution and mass is more complex, it may be desirable to use a more complex function relating the step interval s (t) to the time of flight t.

A preferred embodiment of the present invention will now be described with reference to fig. 1-7.

Figure 1 shows a portion of a mass spectrum obtained by mass analysis of a polyethylene glycol sample. The sample was ionized using a matrix-assisted laser desorption ionization (MALDT) ion source. Mass spectra were acquired using an orthogonal acceleration time-of-flight mass analyzer. The mass spectrum shown in fig. 1 is the result of combining or summing 48 individual time-of-flight spectra generated by firing the laser 48 times (i.e., 48 individual acquisition results were obtained). A 2GHz8 bit analog-to-digital converter was used to acquire or record time-of-flight spectra.

Figure 2 shows a single spectrum over the same range of mass to charge ratios as shown in figure 1. A signal is generated as individual ions arrive at the ion detector.

FIG. 3 shows the result of processing the single spectrum shown in FIG. 2 for a two-pass moving average smoothing function (equation 1) for seven time digitized points using a smoothing window, according to one embodiment of the invention. The smoothed signal is then differentiated twice using a three-point moving window difference calculation (equation 4). The zero crossings of the second order differential are determined as the starting and ending points of the signal of interest within the spectrum. Then, the centroid of each signal is determined using equation 13. The strength of each detected signal and the time determined by equation 14 are recorded. The resulting processed mass spectral data is shown in figure 3 as intensity-time pairs. The accuracy of the centroid calculation for each ion arrival is higher than the accuracy provided by the individual time intervals of the analog-to-digital converter.

Fig. 4 shows the result of combining 48 individual spectra, each of which has been pre-processed using the method described above in connection with fig. 3, according to the preferred embodiment. The 48 sets of processed data comprising intensity-time pairs are combined to form a composite data set comprising a plurality of intensity-time pairs.

Having provided or obtained the composite data set shown in fig. 4, the composite data set is preferably integrated using, for example, a two-pass boxcar integration algorithm in accordance with the preferred embodiment. According to one embodiment, the integration algorithm may have a width of 615ps and a step interval of 246 ns. The resulting integrated and smoothed data set or continuum mass spectrum is shown in fig. 5. It can be seen that the mass resolution and signal-to-noise ratio within the spectrum is greatly improved compared to the raw analog-to-digital converter data or mass spectrum shown in figure 1.

FIG. 6 shows the second order differential of the single processed continuum mass spectrum shown in FIG. 5. The second order differential is derived using a moving window of 1.23 ns. The zero crossings of the second order differential are used to determine the onset and end of mass peaks observed within the continuum mass spectrum.

Fig. 7 shows the final mass-to-charge ratio and the corresponding intensity values obtained according to this preferred embodiment. According to the preferred embodiment, the 48 spectra shown in FIG. 4 are integrated into a continuum mass spectrum, which is then reduced to a discrete mass spectrum. The time of flight for each mass peak is determined using equation (24) and the intensity of each mass peak is determined using equation (21).

For all the spectra shown in fig. 1-7, the time axis has been converted to the mass-to-charge ratio axis using the time-mass relationship derived by a simple calibration process. At the masses shown, an ADC digitization interval of 0.5ns is approximately equivalent to a mass of 0.065 daltons.

According to this preferred embodiment, the time-of-flight detector (secondary electron multiplier) may comprise a microchannel plate, a photomultiplier or an electron multiplier or a combination of these types of detectors.

The digitization rate of the ADC may be uniform or non-uniform.

According to one embodiment of the invention, the calculated intensity I and the time of flight t of several voltage peaks may be combined into a single representative peak. If the number of voltage peaks in the spectrum is large and/or the number of spectra is large, the final total number of voltage peaks may become large. Therefore, combining data in this manner will advantageously reduce memory requirements and subsequent processing time.

A single representative peak may consist of a voltage peak component with a sufficiently narrow time range so that data integrity is not compromised and so that the mass spectrum retains its resolution. It is desirable that the peak or mass peak start and end times can still be determined with sufficient accuracy so that the resulting peak or mass peak consists of the substantially original voltage peak at which such initial peak merging would not occur. The single representative peak preferably has an intensity and time-of-flight that accurately represents the combined intensity and combined weighted time-of-flight of all voltage peak components. The intensity and time of flight of the resulting peak or mass peak are preferably substantially the same regardless of whether some merging of voltage peaks occurs in the data processing.

While the present invention has been described with reference to preferred embodiments, it will be understood by those skilled in the art that various changes in form and details may be made to the specific embodiments discussed above without departing from the scope of the present invention as set forth in the following claims.

Claims

1. A method of mass spectrometry comprising:

determining a time of arrival of one or more first ions from the second differential or the second differential of the first digitised signal;

determining an intensity of the one or more first ions;

determining a time of arrival of one or more second ions from the second differential or the second differential of the second digitised signal;

determining the intensity of the one or more second ions; and is

Determining whether the determined arrival times of the one or more second ions fall within a time period, time window, or memory array cell into which the determined arrival times of the one or more first ions fall, wherein if it is determined that the determined arrival times of the one or more second ions fall within the time period, time window, or memory array cell into which the determined arrival times of the one or more first ions fall, the method further comprises: (i) determining an average arrival time of the determined arrival times of the one or more first ions and the one or more second ions; and/or (ii) determining a combined intensity of the one or more first ions and the intensity of the one or more second ions.

2. The method of claim 1, further comprising digitizing the first signal and/or the second signal using an analog-to-digital converter or a transient recorder.

3. The method of claim 1 or 2, further comprising smoothing the first digitized signal and/or the second digitized signal.

4. The method of claim 1, wherein the step of determining a time of arrival of one or more first ions from the second differential of the first digitized signal comprises determining one or more zero crossings of the second differential of the first digitized signal.

5. The method of claim 1, wherein the step of determining a time of arrival of one or more second ions from the second differential of the second digitized signal comprises determining one or more zero crossings of the second differential of the second digitized signal.

6. The method of claim 1, further comprising determining the intensity and/or moment of one or more peaks present in the first digitized signal and/or the second digitized signal corresponding to one or more ion arrival events.

7. The method of claim 1, further comprising determining a centroid time of one or more peaks corresponding to one or more ion arrival events present in the first digitized signal and/or the second digitized signal.

8. The method of claim 1, further comprising determining an average or representative time of one or more peaks corresponding to one or more ion arrival events present in the first digitized signal and/or the second digitized signal.

9. The method of claim 1, further comprising:

determining or obtaining a second differential or a second difference of the one or more further digitized signals;

determining the arrival time of one or more further ions from the second order differential or the second order differential of the one or more further digitised signals;

determining the intensity of the one or more additional ions; and is

Determining whether the determined arrival times of the one or more further ions fall within a time period, time window or memory array cell within which the determined arrival times of one or more further ions fall, wherein if it is determined that the determined arrival times of the one or more further ions fall within the time period, time window or memory array cell within which the determined arrival times of the one or more further ions fall, the method further comprises: (i) determining an average arrival time of the determined arrival times of the one or more additional ions and the determined arrival times of the one or more other ions; and/or (ii) determining a combined intensity of the one or more further ions and the intensity of the one or more further ions.

10. The method of claim 9, further comprising combining data relating to time and intensity of peaks relating to ion arrival events to provide a continuous time spectrum or mass spectrum.

11. The method of claim 1, further comprising storing the determined time or average time and/or intensity of one or more peaks present in the digitized signal corresponding to one or more ion arrival events.

12. An apparatus, comprising:

means arranged to determine the arrival time of one or more first ions from the second differential or second differential of the first digitised signal;

means arranged to determine the intensity of the one or more first ions;

means arranged to determine the arrival time of one or more second ions from the second differential or second difference of the second digitised signal;

means arranged to determine the intensity of the one or more second ions; and

means arranged to determine whether the determined arrival times of the one or more second ions fall within a time period, time window or memory array cell within which the determined arrival times of the one or more first ions fall, wherein if it is determined that the determined arrival times of the one or more second ions fall within the time period, time window or memory array cell within which the determined arrival times of the one or more first ions fall, the apparatus is further to: (i) determining an average arrival time of the determined arrival times of the one or more first ions and the one or more second ions; and/or (ii) determining a combined intensity of the one or more first ions and the intensity of the one or more second ions.

13. The apparatus of claim 12, further comprising an analog-to-digital converter or a transient recorder to digitize the first signal and/or the second signal.

14. A mass spectrometer, comprising:

the apparatus of claim 12 or 13; and

a mass analyzer selected from the group consisting of: (i) a time-of-flight ("TOF") mass analyzer; (ii) an orthogonal acceleration time of flight ("oaTOF") mass analyzer; or (iii) an axially accelerated time-of-flight mass analyser.

15. A method of mass spectrometry comprising:

determining a mass or mass-to-charge ratio of one or more first ions from the second differential or the second differential of the first digitised signal;

determining an intensity of the one or more first ions;

determining the mass or mass-to-charge ratio of one or more second ions from the second differential or second difference of the second digitised signal;

determining the intensity of the one or more second ions; and is

Determining whether the determined mass or mass to charge ratio of the one or more second ions falls within a mass window or predetermined memory location within which the determined mass or mass to charge ratio of the one or more first ions falls, wherein if it is determined that the determined mass or mass to charge ratio of the one or more second ions falls within a mass window or predetermined memory location within which the determined mass or mass to charge ratio of the one or more first ions falls, the method further comprises: (i) determining an average mass or mass-to-charge ratio of the determined mass or mass-to-charge ratio of the one or more first ions and the determined mass or mass-to-charge ratio of the one or more second ions; and/or (ii) determining a combined intensity of the one or more first ions and the intensity of the one or more second ions.

16. An apparatus, comprising:

means arranged to determine the mass or mass-to-charge ratio of one or more first ions from the second differential or second differential of the first digitised signal;

means arranged to determine the intensity of the one or more first ions;

means arranged to determine the mass or mass-to-charge ratio of one or more second ions from the second differential or second difference of the second digitised signal;

means arranged to determine the intensity of the one or more second ions; and

means arranged to determine whether the determined mass or mass to charge ratio of the one or more second ions falls within a mass window or predetermined memory location within which the determined mass or mass to charge ratio of the one or more first ions falls, wherein if it is determined that the determined mass or mass to charge ratio of the one or more second ions falls within a mass window or predetermined memory location within which the determined mass or mass to charge ratio of the one or more first ions falls, the apparatus is further to: (i) determining an average mass or mass-to-charge ratio of the determined mass or mass-to-charge ratio of the one or more first ions and the determined mass or mass-to-charge ratio of the one or more second ions; and/or (ii) determining a combined intensity of the one or more first ions and the intensity of the one or more second ions.

17. A method of mass spectrometry comprising:

determining a time of arrival of one or more first ions;

determining an intensity of the one or more first ions;

determining the arrival time of one or more second ions;

determining the intensity of the one or more second ions; and is

18. An apparatus, comprising:

means arranged to determine the arrival time of one or more first ions;

means arranged to determine the intensity of the one or more first ions;

means arranged to determine the arrival time of one or more second ions;

means arranged to determine the intensity of the one or more second ions; and

19. A method of mass spectrometry comprising:

determining the mass or mass-to-charge ratio of one or more first ions;

determining an intensity of the one or more first ions;

determining the mass or mass-to-charge ratio of one or more second ions;

determining the intensity of the one or more second ions; and is

20. An apparatus, comprising:

means arranged to determine the mass or mass-to-charge ratio of one or more first ions;

means arranged to determine the intensity of the one or more first ions;

means arranged to determine the mass or mass-to-charge ratio of one or more second ions;

means arranged to determine the intensity of the one or more second ions; and means arranged to determine whether the determined mass or mass to charge ratio of the one or more second ions falls within a mass window or predetermined memory location within which the determined mass or mass to charge ratio of the one or more first ions falls, wherein if it is determined that the determined mass or mass to charge ratio of the one or more second ions falls within a mass window or predetermined memory location within which the determined mass or mass to charge ratio of the one or more first ions falls, the apparatus is further to: (i) determining an average mass or mass-to-charge ratio of the determined mass or mass-to-charge ratio of the one or more first ions and the determined mass or mass-to-charge ratio of the one or more second ions; and/or (ii) determining a combined intensity of the one or more first ions and the intensity of the one or more second ions.