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WO1991005241A1 - Detection d'emission infrarouge - Google Patents

Detection d'emission infrarouge Download PDF

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Publication number
WO1991005241A1
WO1991005241A1 PCT/US1990/005591 US9005591W WO9105241A1 WO 1991005241 A1 WO1991005241 A1 WO 1991005241A1 US 9005591 W US9005591 W US 9005591W WO 9105241 A1 WO9105241 A1 WO 9105241A1
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Prior art keywords
flame
infrared
detector
sample
interest
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PCT/US1990/005591
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English (en)
Inventor
Kenneth W. Busch
Keith M. Hudson
Marianna A. Busch
Sidney Wayne Kubala, Jr.
David Charles Tilotta
Christopher Kwok Yin Lam
Ravishankar Srinivasan
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Research Corp Technologies Inc
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Research Corp Technologies Inc
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Priority claimed from US07/415,141 external-priority patent/US5246868A/en
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Publication of WO1991005241A1 publication Critical patent/WO1991005241A1/fr
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
    • G01N21/71—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light thermally excited
    • G01N21/72—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light thermally excited using flame burners

Definitions

  • This invention relates to infrared emission
  • detection means and method for detecting selected molecules of interest in a gaseous sample or samples which can be converted to the gas phase are particularly applicable to the fields of gas chromatography, liquid chromatography, CO 2 detection, total organic carbon analysis, total inorganic carbon analysis, water analysis,
  • U.S. Patent No. 3,836,255 describes a spectrometric substance analyzer which monitors both emission and absorption.
  • a fluid is cyclically heated and cooled wherein the radiation variation is characteristic of the substance of interest in the fluid.
  • U.S. Patent No. 3,516,745 describes a method for observation of gas spectral emissions.
  • the gas is contained in a chamber where it is cyclically compressed and allowed to expand.
  • the variation in infrared emission can be correlated to the concentration of gas within the piston.
  • oscillation excites or energizes the gas contained in the chamber to give off spectral emissions.
  • 3,516,745 describes an IR emission analyzer where the sample is periodically compressed and expanded.
  • the compressed gas becomes heated due to increased molecular collision and thereby produces infrared emissions.
  • Comparison of the emissions of the compressed and expanded gas produces a differential emission dependent upon gas concentration.
  • the energy radiated from a combustion flame extends from the ultraviolet region of the spectrum to the far infrared region.
  • emission from the ultraviolet and visible regions of the spectrum accounts for only about 0.4% (Gaydon, A. G.; The Spectroscopy of Flames; Chapman and Hall: London, 1974; pp 221-243).
  • infrared emission from a combustion flame may account for as much as 20% of the total energy radiated
  • the longer wavelength band corresponds to the asymmetric stretch of the carbon dioxide molecule
  • the amount of infrared emission observed from flames is also dependent on a number of other parameters. Studies of flames have shown that most of the energy is lost by conduction and convection occurring upon mixing with the cooler atmospheric air (Gaydon, A. G.; The Spectroscopy of Flames; Chapman and Hall: London, 1974; pp. 221-243.) In addition, turbulent flow has been observed to decrease the amount of infrared radiation emitted (Gaydon, A. G.;
  • the region of observation within the flame is an important consideration. Spatially, the emission of infrared radiation is observed to be a maximum in the outer cone and the surrounding gases with little or no emission from the inner conal area (Gaydon, A. G.; The
  • the amount of infrared radiation emitted from the flame is a function of the number of CO 2 and H 2 O molecules present in the hot gases.
  • Figure 1 schematically illustrates the apparatus used in Experiment 1 for the non-dispersive studies.
  • FIG. 1 schematically illustrates the apparatus used in the wavelength-selective studies of Experiment 1.
  • Figure 3 schematically illustrates an optical system for use in Fourier Transform spectrometer studies.
  • Figure 4 schematically illustrates the preamplifier circuit for PbSe detector.
  • Figure 5 graphically illustrates the signal profile as a function of time for a 50 ⁇ L injection of toluene.
  • Figure 6 graphically illustrates the peak height signal as a function of injection volume in microliters for toluene.
  • Figure 7 graphically illustrates the effect of observation height above the burner on the signal when pure ethanol was aspirated into the flame.
  • Figure 8 graphically illustrates the signal obtained per mole of carbon as a function of the number of carbon atoms in the molecule.
  • Figure 9 graphically illustrates the effect of detector bias voltage on the signal observed at 4.3 ⁇ m when 10% methanol/water mixture was pumped into the burner from the liquid chromatograph at 2 mL/minute.
  • Figure 10 graphically illustrates the effect of chopping frequency on the signal observed when pure ethanol was aspirated into the flame at a steady rate.
  • Figure 11.1 - 11.2 are the infrared spectra
  • Figure 12.1 - 12.2 are the infrared spectra
  • Figure 13 graphically illustrates the signal observed at 4.3 ⁇ m as a function of CO 2 flow rate.
  • Figure 14 graphically illustrates the signal obtained at 4.3 ⁇ m as a function of volume of ethanol injected into liquid chromatograph.
  • Figure 15 is the chromatogram obtained when 50 ⁇ L of an equivolume mixture of methanol, ethanol and propanol were eluted from the liquid chromatograph. The order of elution was methanol, ethanol, propanol.
  • Figure 16 schematically illustrates the apparatus used in Example 2.
  • FIG.1-17.3 schematically illustrates the burner assembly for Example 2.
  • Figure 18 is a chromatogram of 5 ⁇ L of unleaded gasoline obtained on 10% OV-101. Column temperature was maintained at 55°C for 4 minutes and then ramped to 200°C over a period of 7 minutes.
  • Figure 19 shows the elution peaks obtained for various volumes of pentane in microliters.
  • Figure 20 graphically illustrates peak height versus volume in microliters for dichloromethane.
  • Figure 21 graphically illustrates peak height versus volume in microliters for trichlorotrifluoroethane.
  • Figure 22 graphically illustrates peak height versus volume in microliters for carbon tetrachloride.
  • Figure 23 graphically illustrates peak height versus volume in milliliters for carbon dioxide.
  • Figure 24 graphically illustrates peak height versus micromoles of compound injected obtained with a flame infrared emission detector for 1, carbon dioxide; 2 , pentane; 3,1,1,2-trichloro-1,2,2-trifluoroethane; 4, dichloromethane; 5, carbon tetrachloride.
  • Figure 25 graphically illustrates the logarithm of peak height versus logarithm of injection volume in
  • Figure 26 graphically illustrates the relative response of a flame infrared emission detector for methane, carbon monoxide and carbon dioxide.
  • Figure 27 graphically illustrates the relative response of a flame infrared emission detector per mole of carbon for various compounds containing different numbers of carbons: BR-ETH, bromoethanol; DI-CL, dichloromethane;
  • TRI-CL tricloromethane
  • TRI-CL EN trichloroethanol
  • N-PENT n-pentane
  • N-HEX n-hexane
  • N-HEPT n-heptane
  • C-PENT cyclopentane
  • C-HEX cyclohexane
  • C-HEPT cycloheptane
  • C-M-HEX methylcyclohexane
  • C-OCT cyclooctane
  • Figure 28 graphically illustrates peak height for carbon dioxide versus carrier gas flow rate obtained with a flame infrared emission detector.
  • Figure 29 graphically illustrates peak area versus carrier gas flow rate obtained with a flame infrared emission detector.
  • Figure 30 shows the chromatogram obtained isothermaliy at 50°C on an Apiezon-L column for a 5- ⁇ L injection of a 1:2:1:3 volume mixture: pentane (1);
  • Figure 32 is a flame infrared emission spectrum of carbon tetrachloride.
  • Figure 33 is a flame infrared emission spectrum of methanesulfonyl fluoride.
  • Figure 34 is a flame infrared emission spectrum of the H 2 /air background at high gain.
  • Figure 35 is a flame infrared emission spectrum of methanol.
  • Figure 36 is a flame infrared emission spectrum of trichlorotrifluoroethane.
  • Figure 37 is a flame infrared emission spectrum of tetramethylsilane.
  • Figure 39 are Fourier-transform infrared spectra from 4000-1800 cm -1 plotted on the same relative intensity scale (not corrected for instrument response) of (A)
  • Figure 40 are hydrogen chloride signal profiles obtained by (A) treatment of an acidified aliquot of an NaCl solution with saturated KMnO 4 and (B) addition of
  • Figure 41 graphically illustrates the HCl flame infrared emission signal versus bromide concentration.
  • Figure 42 schematically illustrates the dual channel system of Experiment 5.
  • Figure 43 schematically illustrates the electronic signal processing module of the dual channel system with optical attenuation.
  • Figure 44 graphically illustrates (A) the selectivity ratio versus detector bias voltage and (B) the detection limit concentration versus detector bias voltage for the dual channel system.
  • Figure 45 schematically illustrates the electronic signal process module of the dual channel system with an adjustable load resistor.
  • Figure 46 schematically illustrates the electronic processing module of the dual channel system with an
  • Figure 47 graphically illustrates peak height versus concentration for the dual channel system in the fluoride sensitive, chloride sensitive and carbon sensitive modes.
  • Figure 48 are flame infrared emission chromatograms illustrating the relative performance of the subtracted and unsubtracted modes of operation in three selective modes.
  • Figure 49 is a chromatograph of a complex mixture utilizing a commercial TCD detector.
  • Figure 50 is a chromatograph of a complex mixture utilizing a flame infrared emission detector in the carbon mode.
  • Figure 51 is a chromatograph of a complex mixture utilizing a flame infrared emission detector in the fluoride selective mode.
  • Figure 52 schematically illustrates the apparatus for a combined infrared and flame ionization detector.
  • the present invention relates to infrared emission detection means and method whereby the infrared emission of excited molecules of interest in a sample is used as a basis for detection of compounds.
  • infrared emission is observed as a means of detection for chromatography.
  • Organic compounds introduced into a flame result in the production of carbon dioxide which allows observation of two strong emission bands over the wavelength from 1 to 5 ⁇ m .
  • Other infrared active species could be produced as well over the entire infrared region.
  • Total inorganic carbon and total organic carbon are important analytical parameters in the environmental characterization of water. Total organic carbon determinations are performed routinely as a non-specific measure of the organic content of water in pollution monitoring. Inorganic carbon exists in water as bicarbonate and carbonate ions and as dissolved carbon dioxide. The sum of these carbon species is called
  • TIC Total Inorganic Carbon
  • TIC can be determined directly by acidification of the sample to convert bicarbonate and carbonate ions into dissolved CO 2 , purging of the sample with a suitable gas to remove the dissolved CO 2 , and measurement of the CO 2 (usually by infrared absorption).
  • inorganic carbon determinations by flame infrared emission detection can be used in place of alkalinity titrations to determine the amount of inorganic carbonate present in a water sample.
  • Infrared emission detection can be used to monitor carbon impurities in electronic grade gases. Carbon/hydrogen characterization of compounds by infrared emission detection is possible by observing the two strong emission bands, one associated with carbon dioxide and one with both water and carbon dioxide. Molecules or molecular fragments containing heteroatoms can be observed by Fourier transform infrared emission spectroscopy. In that many biochemical reactions result in the release of carbon dioxide as a by-product, infrared emission detection can provide the basis for a variety of clinical and biochemical assays.
  • the infrared emission detection system finds application in the determination of chloride and available chlorine in aqueous samples.
  • the chlorine analysis method includes means for pretreating the sample to evolve chlorine gas. Samples containing aqueous chloride are pretreated with a strong oxidant such as permanganate ion, peroxide ion or
  • the infrared emission detector is a flame infrared emission detector wherein the flame is a hydrogen/entrained-air flame.
  • the chlorine gas reacts with hydrogen from the flame to form
  • the HCl is excited by the flame and exhibits a strong, well-resolved emission band which lies between those for water and carbon dioxide.
  • a 3.8 ⁇ m bandpass filter in the infrared emission detector is used to monitor the emission band and subsequently determine the concentration of chloride and available chlorine in the sample.
  • the performance of the basic infrared emission detector is improved two orders of magnitude by the use of a dual beam system with background subtraction capability.
  • the selectivity ratio and detection limits are optimized by adjusting the detector bias voltage, using an optical filter in the reference channel for background compensation and balancing the Wheatstone bridge network.
  • the improved detector can therefore detect smaller quantities of species of interest.
  • a preferred embodiment is the use of the improved detector for the detection of carbon compounds, chlorinated compounds, fluorinated compounds as well as chlorofluorocarbons.
  • the flame ionization detector (FID) is probably the most currently used GC detector. It is surely the most sensitive for organic compounds.
  • a combination infrared detector combining an FID and a flame infrared emission detector provides FID sensitivity and flame infrared emission detection of CO, CO 2 and other compounds.
  • the present invention relates to an infrared detection means and a method for detecting selected molecules of interest in a gaseous sample or samples which can be converted to the gas phase.
  • the infrared detection means includes a detector means and a means for exciting molecules of interest in the sample to emit a characteristic infrared radiation pattern. In one embodiment, heating by a flame is employed to combust and excite the molecules of interest in the sample to produce vibrationally excited molecules such as carbon dioxide which can emit infrared radiation.
  • pre-determined wavelength of infrared radiation emitted by the molecules of interest is observed with a detector by generating an electrical signal in response to the emission at the observed wavelength.
  • the obseiv ation wavelength is preselected from the characteristic infrared radiation pattern of the molecule of interest.
  • the means for isolating a preselected wavelength of infrared radiation is mounted between the exciting and detector means .
  • a factor necessary for successful implementation of infrared emission is to achieve a useful level of contrast between the source and the background, that is the source should be at a higher temperature than the surrounding background, and the temperature of the source should be greater than the temperature of the detector. For this reason, one would not expect to see infrared emission from a gas at room temperature if the background and the detector are also at room temperature. Therefore, the first
  • emission sources for this application if a low-background flame in the vicinity of the selected emission band can be found.
  • excitation means include: 1) other thermal excitation such as a furnace excitation;
  • Photoexcitation with an appropriate source.
  • Photoexcitation can be accomplished from the 000 level of CO 2 (resonance excitation) or from the 010 level which is appreciably populated even at room temperature (non-resonance
  • a second requirement for high sensitivity is the avoidance of the use of any form of solid containment such as a sample cell.
  • the infrared emitting source i.e., the gas in this case
  • the background As a result of a thermal gradient.
  • the emission signal which is initially present from the gas because it is hotter than the walls of the cavity , gradually fades into the background until it disappears.
  • previous experiments had to employ complicated recirculating systems so that hot gases and cold gases could be alternately admitted into the sample cell at a rate sufficiently great that the system would not have time to reach thermal equilibrium (i.e., use of thermal cycling).
  • the hydrogen/air flame is more convenient because it has a lower burning velocity which makes it easier to design a burner which will not flash-back (i.e., explode).
  • the hydrogen/oxygen flame may produce a larger signal because of its higher temperature.
  • one of the carbon dioxide emission bands is overlapped with two water emission bands in the hydrogen/air flame (producing a composite band at 2.7 ⁇ m)
  • the region at 4.3 ⁇ m where the only other carbon dioxide emission occurs is clear of any other potentially interfering flame background.
  • the hydrogen/air flame was selected as an excitation source for preliminary studies of flame infrared CO 2 emission. Many detectors sensitive in the infrared are also sensitive in the UV/visible, although they are generally not used in this region because they are considerably less sensitive than other available detectors such as the
  • the photomultiplier is based on the
  • the photon absorbed by a suitable photoemissive material is ejected from the material into the surrounding vacuum.
  • the photon absorbed must possess an energy greater than the sum of the energy bandgap and electron affinity of the photoemitter.
  • Detectors based on photoemission of electrons as a result of the photoelectric effect can be made very sensitive by the use of electron multiplication with a dynode chain.
  • photomultipliers can be made so sensitive that they are often limited by the fluctuation in the arrival rate of photons rather than fluctuations arising within the detector itself.
  • photomultipliers is confined essentially to the UV/visible region of the spectrum. By reducing the electron affinity of certain photoemitters, photomultipliers that respond to longer wavelengths beyond the visible (out to about 950 nm) have been produced.
  • Thermal detectors respond to the heating effect of the infrared radiation and include
  • thermocouples thermocouples, thermistors, and pyroelectric detectors.
  • Quantum detectors make use of the internal photoelectric effect whereby an electron is promoted from the valence band to the conduction band but is not ejected from the material.
  • these detectors respond out to wavelengths whose energies correspond to the semiconductor bandgap.
  • These detectors include photovoltaic and photoconductive detectors.
  • Neither category of detector discussed above employs any form of internal amplification comparable to the photomultiplier and for this reason, IR detectors are less sensitive than detectors commonly used for the detection of UV/visible radiation. Since the major source of noise with these detectors originates within the detector itself and is not due to fluctuations in the radiation field, these detectors are frequently cooled to reduce detector noise, and
  • quantum detectors generally have a higher specific detectivity than thermal detectors, although thermal
  • detectors have the advantage of flat response over a wide wavelength range. For the applications under consideration, a detector which did not require cooling to dry ice or liquid nitrogen temperatures was desired. For the wavelength region under consideration (2-5 ⁇ m), the lead selenide and indium antimonide detectors were two possibilities. Of the two, the indium antimonide had the higher specific detectivity but generally required cooling. For this reason, the PbSe
  • thermoelectric cooling was selected as the most appropriate for preliminary studies on the basis of spectral response and cost. Even with the PbSe detector, however, some thermoelectric cooling may be beneficial to shift the maximum response of the
  • the reason that absorption measurements are less sensitive than the corresponding emission experiment is due to the fact that as the detection limit is approached, the absorbance, which is the logarithm of the ratio of the incident beam intensity to the transmitted beam intensity, approaches zero. This means that the magnitude of the transmitted beam intensity approaches the magnitude of the incident beam intensity.
  • the question of detection then revolves around whether it is possible statistically to tell the difference between these two large numbers. It is well known from statistics, that differences between two large numbers, which are close to one another in magnitude and which fluctuate, are often not significant.
  • emission by contrast, the detection limit occurs when the signal cannot be statistically distinguished from the background. Since the background is hopefully small, this situation is
  • emission measurements are usually linear over a much wider range of concentrations.
  • use of emission measurements rather than absorption measurements is based on sound analytical reasoning and is not simply an alternative way of
  • Process gases are those gases used in manufacturing and electronic-grade gases in particular are those gases used in the manufacture of electronic devices. Impurities such as CO, CO 2 , and trace hydrocarbons in gases used in the
  • the infrared emission detector has good sensitivity to CO, CO 2 , and the light gaseous
  • This stream measures the total impurity concentration (i.e.,
  • a second stream passes first through a bed of a CO absorbent prior to entering a second infrared emission detector. This stream measures the sum of the CO 2 and hydrocarbons (S 2 ).
  • a third stream passes first through a bed of CO 2 absorber (Ascarite) prior to entering a third infrared emission detector. This stream measures the sum of the CO and hydrocarbons (S 3 ).
  • the signals from the three streams relate to the impurity concentrations as follows:
  • the infrared emission system has a multiplex advantage over systems which measure one component at a time.
  • infrared emission technology is for water analysis. This includes drinking water (potable water), environmental samples, wastewater, and even clay-based drilling muds used in petroleum production (i.e., oil rigs). This application falls into two major categories: total inorganic carbon- and organic carbon determinations.
  • the carbonate concentration is determined indirectly by means of alkalinity titrations.
  • the alkalinity of a water sample is determined from the proton condition of the solution as
  • K 1 K 2 /D and K 1 and K 2 are the first and second dissociation constants of carbonic acid.
  • the alkalinity of a water sample is also a measure of the acid neutralizing capacity of the solution.
  • the total alkalinity of a water sample is determined.
  • the total inorganic carbon or C T is determined from a knowledge of the alkalinity by rearranging the alkalinity relationship:
  • sulfuric acid 0.5 mL
  • a water sample (1 mL) is added to release carbon dioxide gas which is flushed with helium into a hydrogen/air flame.
  • the infrared emission from carbon dioxide is measured with an infrared emission detector as described previously.
  • a calibration curve prepared from standard carbonate solutions is used to determine the total inorganic carbon concentration in the sample.
  • Infrared emission detection is also useful in determining the carbon dioxide content in carbonated
  • beverages such as soft drinks and beer.
  • Organic materials in water samples may arise from naturally occurring compounds produced by living organisms or from anthropogenic sources. The sum of the naturally occurring compounds
  • the total organic carbon in the water sample is referred to as the total organic carbon in the water sample.
  • the total organic carbon content of a sample is a non-specific (i.e., doesn't determine the actual individual compounds present) measure of the organic content of the sample.
  • Total organic carbon (TOC) determinations are performed on a wide range of samples, including ground water, drinking water, semiconductor process water, municipal wastewater, and industrial wastewater (Small, R.A. et al.,
  • TOC determinations include determination of organic contamination in mineral products such as acids, caustic solutions, as well as aluminum-, nickel-, and cobalt chlorides.
  • Power generation plants use TOC measurements to determine organic contaminants in cooling water and
  • TOC determinations have been used to monitor surface water, ground water (i.e., wells), and other water sources for wastewater contamination and industrial effluents.
  • TOC determinations are performed by first or dizing the organic material to carbon dioxide by a variety of methods (Small, R.A. et al., International
  • NDIR absorption spectrophotometry
  • carbon dioxide is produced by the same methods currently used to oxidize organic materials to CO 2 .
  • oxidation methods include one or a combination of the following: chemical methods such as the use of peroxydisulfate, heating such as in a furnace with copper oxide and the use of UV radiation.
  • the CO 2 is flushed out of the sample to the infrared emission dete tor.
  • the sample may be combusted directly in the flame to generate CO 2 .
  • infrared emission instead of absorption of CO 2 the interference by other concomitants produced by the oxidation process is avoided. Since the infrared emission detector is not affected by water vapor and acid gases, these interferences are absent with the infrared emission TOC analyzer. Since the infrared emission system employs a filter, it falls in the category of non-dispersive infrared analysis (only in emission rather than absorption). Since two strong emission bands are observed in the flame, one corresponding to the asymmetric stretching
  • a carbon to hydrogen ratio instrument is useful for combustion monitoring, as in smoke stack and rocket engine firing monitoring.
  • the infrared emission is useful as a detector in conventional carbon/hydrogen analyses (as opposed to using it as a detector in chromatography).
  • the infrared emission system is used as the detection means in the analysis.
  • an instrumental carbon/hydrogen analyzer can use conventional combustion tube techniques to transform the organic material into water and carbon dioxide. The infrared emission is then used to detect the amounts of these materials which have been generated.
  • the element chlorine is widely distributed in nature and is used extensively in its various oxidation states.
  • Aqueous elemental chlorine (Cl 2 ) and hypochlorite (OCl-), for example, are employed as bleaching agents and as disinfectants to prevent the spread of waterborne diseases.
  • OCl- hypochlorite
  • the element occurs in nature primarily as the chloride ion (Cl-) and is one of the major inorganic
  • chloride levels expressed as chlorinity, are approximately related to salinity and can be used to determine the concentrations of all other
  • chloride concentrations in the sewerage of coastal areas may signal seawater intrusion into the system, while in potable water they are often associated with wastewater contamination. In process waters, chloride concentrations are monitored regularly since
  • elevated levels are generally associated with increased deterioration of metallic pipes and structures, while in cooling water, they are used to indicate the cycles of concentration.
  • argentometric methods For the titrimetric determination of aqueous chloride, various argentometric methods exist which use either indicators or potentiometers to detect the endpoint. Alternatively, mercuric nitrate can be used to titrate chloride ion using diphenylcarbazone as an indicator.
  • iodometric titration is the method of choice. For chlorine levels less than this amount,
  • amperometric titrations are preferred, but require greater operator skill to avoid loss of chlorine through mechanical stirring. Poor endpoints are also a problem unless the electrodes are properly cleaned and conditioned.
  • N,N-diethyl-p-phenylenediamine can be used to determine dissolved chlorine colorimetrically or titrimetrically using ferrous ammonium sulfate.
  • infrared emission detection under high resolution conditions provides spectra wherein the P and R branches of the HCl infrared emission can be easily detected above the flame background in the region from 3200-2400 cm -1 . Since the HCl emission band lies between the water emission band at 3800-3200 cm -1 and the carbon dioxide emission band centered at approximately 2262 cm -1 , the strong, well-resolved infrared emission from HCl should also be useful analytically for the determination of Cl in a variety of chlorine-containing samples.
  • resulting chlorine gas could then be purged from solution using an inert gas and introduced into a hydrogen-air flame to form excited HCl which could be detected by means of its infrared emission.
  • OCl- + H 2 O HOCl + OH- and the term available chlorine refers to the total oxidizing power of the solution due to chlorine, hypochlorous acid and hypochlorite ion, expressed in terms of an equivalent
  • the signal is improved by two orders of magnitude with the use of the improved dual beam system.
  • selectivity ratio and detection limitd can be optimized by varying the detector biad voltage, by use of a 3.0 ⁇ m filter for background compensation, an optical attenuation method to balance the bridge network, and a variable bridge resistor.
  • Figure 1 shows the experimental arrangement used for the initial non-dispersive studies using thermistor detection.
  • a Varian Techtron burner assembly 10 was used as a nebulizer and to provide the sample introduction system.
  • a Meker burner head producing a flame 11 with a diameter of 1.5 cm was designed and fitted to the burner assembly.
  • Initial studies of the infrared emission from a hydrogen/air flame 11 were made using various thermcflake thermistors 12
  • Thermometrics Inc. Edison, NJ mounted in a detector head/housing unit on a test setup facing the burner.
  • a metal tube was attached to the detector housing to limit the field of view of the thermistor flake.
  • the thermistors 12 and 13 were
  • Figure 2 shows the experimental arrangement employed for the dispersive wavelength-selective studies using PbSe detector 24.
  • the IR detection system used in this study was assembled using devices and equipment from various manufacturers as listed in Table I.
  • a Spex 0.5-m Czerny-Turner monochromator (Spex Industries, Inc., Metuchen, NJ) is used as the primary wavelength dispersive device or isolation means.
  • the monochromator is equipped with a 150 groove/mm grating blazed for 4 ⁇ m.
  • a 3-mm entrance slit was used.
  • the wavelength scale of the Spex 1870 monochromator was calibrated by the manufacturer for a 1200 groove/mm grating.
  • measurements of grating rotation versus counter setting were made. These measurements, combined with the geometric arrangement of the mirrors, enabled the wavelength corresponding to a given counter setting to be calculated by means of the grating equation.
  • ⁇ d [sin (r - ⁇ 4 ) + sin (r + ⁇ 2 ) ]
  • m is the order, is the wavelength
  • d is the grating constant
  • r is the rotation angle of the grating.
  • ⁇ 2 is the angle of reflection of the chief ray from the collimating mirror
  • ⁇ 4 is the angle of incidence of the chief ray on the focusing mirror.
  • ⁇ 2 and ⁇ 4 are constants.
  • a Hamamatsu lead-selenide photoconductive cell 24 with integral thermo-electric cooling (P2038-01, Hamamatsu Corp., San Jose, CA) was employed as the infrared detector.
  • Table II lists the specifications of this particular device.
  • a housing/mounting assembly was fabricated so that the detector, 24 in Figure 2, could be mounted in the focal plane of the monochromator with the preamplifier electronics in close proximity.
  • a 30.0 volt regulated power supply was used initially as the power supply for the detector 24.
  • the preamplifier circuit consisting of a BIFET operational amplifier 46 and associated components, is shown in Figure 4.
  • the amplified signal from the preamplifier was applied to the input of a Princeton Applied Research Model 128A lock-in amplifier (Princeton Applied Research, Princeton, NJ), not shown.
  • the radiation from the flame was modulated with a Princeton Applied Research Model 125A variable speed chopper (Princeton Applied Research, Princeton, NJ) at a chopping frequency of 86 Hz.
  • Output from the lock-in amplifier was displayed on a Varian Aerograph stripchart recorder.
  • the PbSe detector 24 was used in all studies utilizing the monochromator.
  • Wavelength-selective studies were also conducted with a high-pass filter in conjunction with the PbSe detector 24 in Figure 2 to isolate the 4.3 ⁇ m emission band.
  • a high-pass filter Corion Corp., Holliston, MA
  • a short wavelength cutoff of 3.5 ⁇ m was mounted in a housing in front of the PbSe detector 24. Since the long wavelength response of the detector 24 only extends out to about 5 ⁇ m (See Table II), this arrangement effectively isolates the 4.3 ⁇ m band without the need for a
  • Varian Techtron burner assembly 20 (Varian Instruments, Palo Alto, CA) used for the non-dispersive studies is also used as the sample introduction system in the dispersive studies.
  • a flame shield is constructed of sheet stainless steel and attached to the burner assembly to minimize the effect of drafts on the flame.
  • the liquid chromatograph used in this study was a Varian Model 5000 (Varian Instruments, Palo Alto, CA), equipped with a MCH-5 reverse-phase column.
  • the interfacing of the Model 5000 and the Varian burner assembly 20 was accomplished initially by simply attaching a polycarbonate tube of similar diameter to the stainless steel outlet tube of the MCH-5 column by means of a zero volume stainless steel coupler. After initial experimentation and testing, a telfon T-coupler 26 was added. This allowed other solvents to be mixed with the chromatographic effluent prior to aspiration by the burner 20.
  • the purpose of the coupler 26 is to improve sample aspiration by the burner/nebulizer 20 by mixing the chromatographic effluent with water prior to nebulization; alternatively, the same device permitted the direct introduction of column effluent into the burner 20 without prior mixing with water if desired. All chromatographic results reported are obtained using the T-coupler 26.
  • Methanol and water are used as the solvents in all chromatographic runs.
  • the methanol is HPLC grade and the water is triply deionized. All standard compounds are reagent grade.
  • Chromatographic runs were done using various mixtures of methanol and water as well as pure water as the eluent. Injection loops of either 10 or 50 microliter volume were employed in all runs. Samples were prepared from mixtures of pure compounds and were loaded into the sample loop using a 1-mL syringe. Samples were introduced onto the column by means of the conventional rotary valve. All runs were done using water as the make-up solvent 27 in the
  • T-coupler 26 prior to aspiration by the burner assembly 20.
  • Initial non-dispersive studies aimed at determining the feasibility of monitoring infrared emission from a combustion flame were conducted using thermistor detectors.
  • the flake thermistors used in this study fall in the category of thermal detectors as described in Putley (Putley, E.H. In
  • flake thermistors are more sensitive than their nonflake counterparts, they were not found to be sensitive enough to detect the levels of infrared energy present when the radiation from the flame was dispersed by the 0.5-m monochromator. This lack of response in the dispersive mode is attributed, at least in part, to the relatively high dispersion obtained with the 0.5-m
  • the effluent from a chromatograph is analyzed by fast Fourier
  • a burner/nebulizer 30 is used for vaporizing and exciting liquid chromatograph effluent sample.
  • the burner assembly 30 may be either the burner previously discussed with respect to Figure 2, or the burner assembly illustrated in Figures 16 and 17, as will be hereinafter discussed in detail with respect to Experiment 2.
  • the emitted infrared radiation is focused by a three mirror assembly 32 through lens 39 and thereby directed into an interferometer 34 intrinsically having an amplifier and infrared detector.
  • the distance between lens 39 and interferometer 34 is about 10 cm.
  • the output of the interferometer 34 is connected to a computer 38 to analyze the collected data by a Fast Fourier
  • Figure 5 shows the signal profile obtained as a function of time for a 50 ⁇ L injection of toluene.
  • Figure 6 shows a plot of signal (i.e., peak height) as a function of injection volume in microliters. Similar plots were obtained for injections of various volumes of methanol.
  • Figure 8 shows the signal per mole of carbon as a function of the number of carbon atoms in the molecule at a particular observation height. If all the compounds
  • the compound depends on the number of carbons in the compound as well as the compound type.
  • the decrease in response observed with the longer chain compounds is probably a result of incomplete combustion of the compound to carbon dioxide.
  • the difference in response between saturated and aromatic compounds is undoubtedly a result of differences in the ease and extent of combustion. Regardless of the actual mechanism ofsignal production, it is clear that the response of the system is compound dependent. As a result,
  • a PbSe photoconductive detector was evaluated using the apparatus illustrated in Fig. 2. These detectors are about two orders of magnitude more sensitive than the thermistor and respond over the wavelength range from 1 to 5 ⁇ m. Other detectors suitable for flame infrared emission detection are indium antimonide and mercury cadmium telluride. For this embodiment, the lead selenide detector wasselected on the basis of the cost effectiveness. Since PbSe detectors are intrinsic semiconductors (i.e., not doped), the long wavelength response cutoff is determined by the inherent energy gap between the valence band and the conduction band. (Boyd, R.
  • the peak response is shifted to longer wavelengths.
  • the dark resistance and time constant also change with cooling. For example,
  • cooling causes the dark resistance to increase by 2.5%/°C and the time constant to increase by 5.3%/°C. Cooling with dry ice
  • Figure 10 shows the results of this study. From the figure, it can be seen that the maximum signal is obtained for a chopping frequency of about 90 Hz. On the basis of thisstudy, a chopping frequency of 86 Hz was employed in all studies in Experiment 1 with the PbSe detector.
  • the 0.5-m monochromator used in this study was selected solely on the basis of its availability in the laboratory and not on the basis of optical considerations.
  • the dispersion system When equipped with a 150 groove/mm grating, thesystem had a reciprocal linear dispersion of 13 nm/mm which is much lower than is necessary for infrared work of the type described here. Furthermore, since the entrance slit was wider (3 mm) than the width of the PbSe detector (1 mm), the dispersion system was characterized by a trapezoidal slit function with a base equivalent to 0.04 ⁇ m and a flat peak equivalent to 0.01 ⁇ m. In spite of the non-ideal slit function, the effective spectral bandwidth of the system was much less than the halfwidth of the molecular emission bands
  • a hydrogen/air flame was selected because of its low background in the vicinity of the 4.4 ⁇ m CO 2 band.
  • Figure 11 shows a comparison of the spectra obtained with the system for an hydrogen/air flame and an acetylene/air fl ame using the PbSe detector.
  • the spectrum obtained with the acetylene/air flame is typical of the results obtained when a carbon-containing fuel is used and is in agreement with the spectrum obtained by Plyler (Plyler, E.K.; J. Res. Nat. Bur.
  • the band at 2.7 ⁇ m is due to both water and carbon dioxide and is therefore present in both flames.
  • the monochromator was replaced by a high-pass optical filter in an effort to increase sensitivity by increasing optical throughput.
  • the wavelength response of the system was limited at lower wavelengths by theshort-wavelength cutoff of the filter and at higher wavelengths by the response of the detector itself.
  • the substitution of the filter for the monochromator resulted in an increase in sensitivity of about
  • the infrared emission at 4.4 ⁇ m provides a sensitive means of detecting small amounts of organic samples introduced into the flame. Since the emission wavelength does not vary, a relatively low-cost filter instrument can be constructed to monitor the desired emission. The detector issuitable for application to both liquid and gas
  • the chromatograph is in some respects easier than with a liquid chromatograph because of the absence of the background signal from the eluent which is present when methanol/water mixtures are used.
  • the dual beam system can be used to remove the presence of interfering background from the eluent.
  • FIG. 16 The experimental arrangement used in this second study isshown in Figure 16.
  • a Hamamatsu lead s elenide photoconductive cell (P2038-01, Hamamatsu Corp., San Jose, CA) was employed as the infrared detector, and was positioned to view a hydrogen/air flame maintained on a specially designed burner 160 described below.
  • a high-pass filter 168 (Corion Corp., Holliston, MA) with a short wavelength cutoff of 3.5 ⁇ m was mounted in a housing in front of the PbSe detector 164 as described in Experiment 1 to give a detection system with a response from 3.5 ⁇ m to about 5 ⁇ m.
  • the power supply and pre-amplifier circuit used in this study for the detector were also as described in Experiment 1. Radiation from the flame was modulated at 90 Hz by a chopper 165 which was constructed in the laboratory. The modulated signal was applied to the input of a Model 128A Princeton Applied
  • Aerograph gas chromatograph (Varian Instruments, Palo Alto,
  • shut-off valve were installed in the gas line of the helium supply. All carrier gas metering was done upstream of the GC and column.
  • the temperature of the GC oven was maintained at a sufficiently high value to avoid sample interactions with the stationary liquid phase as the sample passed down the column. This procedure minimized any column effects which might alter the readings obtained in these studies.
  • solutions of the compound of interest were prepared in a solvent with a higher boiling point than the sample which could be easilyseparated from thesample by the column. The temperature of the oven would then be held above the boiling point of the compound of interest, but below that of thesolvent in order to maximizeseparation and minimize column effects on the sample.
  • the chromatogram obtained for unleaded gasoline was obtained by holding the column temperature at 55°C for 4 minutes and then ramping the temperature up to 200°C over a period of 7 minutes.
  • a special burner shown schematically in Figure 17 was designed to produce a small hydrogen/air pre-mixed flame.
  • the burner was machined from a block of aluminum, and
  • the burner system described in this application produces a stable flame of small size by means of an array ofstainless steel capillary tubes 174. These tubes 174 were cut to a length of approximately 2.5 cm and permitted the use of very low hydrogen/air support gas flow rates without problems from flashback.
  • the combustion gases issued from the burner head through the circular array ( Figure 17.1) of six stainless steel capillaries of 0.10" OD and 0.06" ID which were cemented in a small hole in the burner head by means of epoxy cement.
  • six capillaries arranged in a circular array were used to form the orifice for the combustion gases.
  • the circular array of capillaries surrounded a central capillary 175 through which flowed the column effluent directly into the center of the hydrogen/air flame and which, thereforeserved as a connection between the burner and the gas chromatograph.
  • the central capillary 175 was bent at a right angle to exit the burner body through a side port 176, and was held in place by a rubber seal in a tubing fitting.
  • the new burner design has several important advantages which should be emphasized. Because the rate of sample addition to the flame is determined solely by the carrier gas flow rate and not by the combustion gas flow rates, the rate of sample addition to the flame may be varied independently of the combustion gas flow rates, thereby avoiding changes in the flame size or stoichiometry. By introducing the sample directly into the flame from the central capillary, peak broadening associated with mixing chambers is avoided. Since the capillary has a small
  • post-column volume can be kept to a minimum (0.5 mL/30 cm length of tubing).
  • use of a narrow-bore capillary leads to a high linear velocity gas jet which travels up the center of the flame.
  • a carrier gas flow rate of 40 mL/min. for example, results in a linear velocity in the capillary of 40 cm/s.
  • the transit time for the eluted sample through the 30 cm length of exposed capillary, which runs from the end of the GC column to the flame is about 750 ms. The linear velocity appears to be sufficient to avoid sample
  • carrier gas flow rates used in this study resulted in a gas velocity in the effluent capillary which was so high that thesample components did not havesufficient time to condense on the walls.
  • typical carrier gas flow rates of 30 to 40 mL/min. were used, flows as low as 10 mL/min. were employed without any problems.
  • the fuel-to-oxidant ratio used corresponds to a nearly stoichiometric mixture, and gave the smallest possible flame consistent with good signal conditions. The best
  • Figure 19 shows the shape of typical peaks obtained from the system when various volumes of pentane were injected into the chromatograph as neat samples.
  • Figures 20, 21 and 22 show plots of peak height versus injection volume for dichloromethane
  • the calibration curve for carbon dioxide shown in Figure 23 was prepared to confirm that the phenomenon that was being observed by the detector was, in fact, the emission from carbon dioxide, and also to show that the signal obtained varied linearly with the amount of carbon dioxide introduced. It should be noted that the data shown in Figure 23 indicate a linear relationship between peak height and sample volume in contrast to the results obtained in the previous study using the atomic absorption burner. It is felt that the linear relationship obtained in the present study is due to the use of thesmaller flame, the smaller amounts of carbon dioxide injected, and the method of sample introduction.
  • Figure 24 shows five calibration curves obtained for carbon dioxide, pentane, 1,1,2-trichloro-1,2,2-trifluoroethane, dichloromethane, and carbon tetrachloride.
  • points represent single injections; average
  • Table III shows the reproducibility of response in terms of peak height obtained for a series of 1- ⁇ L
  • Figure 25 shows a log-log plot of chromatographic peak height versus sample volume of pentane introduced into the chromatograph for sample volumes ranging from 0.02 up to 50 ⁇ L . Sample volumes greater than 0.5 ⁇ L were introduced into the
  • Figure 25 shows the response obtained from the lowest level up to injections of approximately 20- to 30- ⁇ L volume, where some downward curving takes place. This downward curving of the calibration curve could be due toseveral factors
  • response data were collected for several series of compounds available in the laboratory and compatible with the GC column used.
  • the compounds used were classified into several categories on the basis of their structure, and includedsubstituted methanes and ethanes as well as n-alkanes and cycloalkanes.
  • Gaseous compounds such as methane, carbon monoxide and carbon dioxide were studied by injecting 500 ⁇ L of the compound with a gas syringe.
  • the response for various liquid compounds was obtained by injecting 1 uL of the neat liquid.
  • the relative response per mole of carbon was calculated from the inj ection volume , the density of the liquid, the formula weight of the compound and the number of carbons in the compound.
  • Figure 26 shows the relative response obtained for equal volumes (i.e., equal moles) of one-carbon gases. If both methane and carbon monoxide were completely combusted to carbon dioxide in the flame, their response would be expected to equal that obtained for an equivalent amount of carbon dioxide. Since the datashown in Figure 26 appear to be equal within experimental error, itsuggests that the
  • Figure 27 shows the relative response obtained per mole of carbon as a function of the number of carbons present in 15 compounds.
  • Table IV shows the actual data obtained for
  • Figure 27 shows that roughly the same relative response was obtained regardless of the number of carbons in the compound out to carbon numbers of about seven. Thissuggests that, if not completely combusted to carbon dioxide, all of the compounds studied with the exception of the two mentioned above are combusted to about the same extent with very little influence of carbon number or compound structure.
  • the exceptions to this rule obtained for cycloheptane and cyclooctane may be more apparent than real because the peak shapes obtained for these compounds were not symmetric. As a result, the use of peak height as a quantitative measure of the signal produced may not have been a reliable indication of the actual peak area.
  • the mass-flow rate detector model predicts that peak signal will increase directly with carrier gas flow rate and the integrated peak area will be independent of carrier gas flow rate.
  • Figure 29 shows that for carrier gas flow rates above 30 mL min -1 , chromatographic peak area varies only slightly with increasing carrier gas flow rate. Apparent deviations from mass-flow rate behavior can be attributed to flame cooling, incomplete mixing, and dilution. As the carrier gas flow rate increases,
  • the detection limit will depend on the limiting base-line noise and the response of the detector.
  • Mass flow rate expressed as mgs -1 , is determined by
  • TCD conductivity detector
  • C dl (mg mL -1 ) 2 (rms base-line noise)/RF (4)
  • F is the carrier gas flow rate in mL s -1
  • C dl is the lowest concentration that the detector can sense. Since the rms base-line noise observed is dependent on the amplifier time constant, it is important to specify the time constant of the system when reporting the detection limit. With eq 3, the detection limit for pentane was determined from detector response measurements and estimates of the rms base-line noise to be 4.6 x -10 -4 mgs -1 for an amplifier time constant of 3 s. The rms noise was estimated as one-fifth of the peak-to-peak base-line noise. In terms of concentration of sample entering the detector for a 40 mL min -1 carrier gas flow rate, the minimum detectable
  • Figure 30 shows the performance of the flame infrared emission system under isothermal conditions for a synthetic sample consisting of a 1:2:1:3 volume mixture of pentane, 1,1,2-trichloro-1,2,2-trifluoroethane, hexane, and carbon tetrachloride.
  • This chromatogram was obtained from a 5- ⁇ L injection of this mixture with an Apiezon L column maintained at 50°C. Since the PbSe detector can respond to intensity variations in the kilohertz range, the flame infrared emission detector has no difficulty in following the relatively slow intensity variations produced during elution of components from the gas chromatograph.
  • the flame infrared emission detection system has been shown to be a relatively simple, inexpensive detector for gas chromatography. Compared with other detectionsystems currently employed, the use of infrared emission has a number of advantages. Since the system is not based on thermal conductivity, nitrogen or hydrogen can be used as a carrier gas in place of the more expensive helium required with a thermal conductivity detector. The system described in this application has been shown to exhibit a wide dynamic range characteristic of emission measurements. The detector has a relatively fast response time which is a potential asset in being able to detect narrow chromatographic peaks as might be obtained with capillary column gas chromatography.
  • the detection systems described above appear to respond to carbon dioxide produced by the combustion of compounds introduced into the flame, and do not appear to be greatly affected by the structural nature of the samples. They also respond to certain gases such as carbon monoxide and carbon dioxide which do not respond well with the flame ionization detector.
  • the miniature capillary-head burner of Experiment 2 was modified for use with liquid samples. As the previously designed burner was intended to admit a gas stream from the gas chromatograph to the center of the burner-head, the burner was modified for nebulized liquid samples. The centralsample injection capillary was removed, and the number of small-bore capillary tubes in the burner-head was increased from 6 to 19 (the internal diameter of the
  • capillary tubes was 0.6 mm). The overall diameter of the burner orifice was 0.5 cm.
  • the capillary-head burner was fitted with a Jarrell-Ash model X-88 atomic absorption cross-flow nebulizer and a 3 cm long x 4 cm diameter teflon spray chamber.
  • the nebulizer and spray chamber were coupled to the burner body by boring a one inch hole in the side of the burner body (perpendicular to the capillary-head) and press fitting the spray chamber/nebulizer assembly to the burner.
  • the Fourier transform spectrometer by virtue of the multiplex nature of the data acquisition, is a multichannel instrument and can therefore monitor all infrared wavelengths simultaneously. Since the desired molecular emission occurs in
  • any standard, commercially available Fourier transform-spectrometer can be utilized without the need for special optics, beamsplitters, or detectors.
  • the Fourier transform instrument also provides several advantages for infrared emission spectroscopy. These advantages include: a single instrument for both elemental and molecular analysis, high optical throughput, good
  • Figure 31 schematically shows the arrangement of the burner 310, mirror 312 and Fourier
  • 5-cm-focal-length, 10-cm-diameter aluminum mirror 312 was used to collect and collimate the infrared emissions from the flame. It should be noted that the infrared collection mirror 312 was placed off the optical axis by approximately 30 degrees. No significant abberational defects were
  • the hydrogen/air flame was chosen to excite the molecules of interest in order to eliminate carbon dioxide emissions from the fuel gases. Otherwise, the determination of carbon, as carbon dioxide, would be significantly
  • Figures 32-37 are characteristic infrared emission spectra for carbon tetrachloride, methanesulfonyl fluoride, the H 2 /Air flame background, methanol, trichlorotrifluoroethane and tetramethylsilane. These spectra clearly show that bands other than those from H 2 O and CO 2 can be observed in the flame.
  • the chlorine sensitive flame infrared emission detection instrument is shown in Figure 38.
  • the instrument consists of a chlorine generation and liberating apparatus and a flame infrared emission detection system.
  • the chlorine generation and liberating apparatus contains two purge devices 387 and 388 (model #991710, Wheaton Scientific,
  • One of the purge tubes serves as the sample chamber 387 while the second serves as the reference chamber 388.
  • Each purge device consists of a 5-mL demountable tube that can be disconnected for sample introduction and cleaning.
  • a septum 381 located at the top of each purge tube allows the samples and reagents to be introduced bysyringe
  • Helium gas maintained at a flow rate of 130 mL/min, was used to purge evolved Cl 2 from the aqueous solutions into the flame 382 of the flame infrared emission detector.
  • capillary-head burner 383 was determined to be 324 mL/min with combustion supported only by entrained air.
  • the supply pressures of the helium and hydrogen were were regulated at
  • This back collection mirror 384 in conjunction with the CaF 2 lens 385, directed the infrared emission from the flame onto the PbSe detector 386.
  • the flame infrared emission detector was also modified by replacing the 4.4 ⁇ m CO 2 optical
  • optical bandpass filter 391 Model # S-902-079, Spectrogon, Secaucus, NJ tospectrally isolate a portion of the HCl emission consisting of most of the more intense part of the R branch.
  • This optical bandpass filter 391 possessed a full-width at
  • the flame infrared emission was detected using a
  • PbSe photoconductive cell operated at room temperature with a bias potential of 45 V.
  • the detector preamplifier circuit, lock-in amplifier and recorder/integrator have been
  • a stock solution of 100 mM NaCl (Mallinckrodt, Inc., St. Louis, MO) was prepared by dissolving NaCl, dried at 120°C for 24 hours, in deionized water. Standard NaCl solutions, having concentrations of
  • the flame in the flame infrared emissionsystem was ignited, and the instrument was allowed to warm up until a stable baseline was obtained on the chart recorder. As part of the warm-up procedure. He purge gas was directed through the dry reference purge tube and into the flame. When the instrument hadstabilized, the analysis for aqueous chloride or available chlorine was carried out according to the appropriate procedure indicated below.
  • the sample purge tube 387 was disconnected, a 1.0-ml volume of an aqueous chloride standard was placed on the glass frit 392, and a 0.5-mL volume of concentrated H 2 SO 4 was added using a syringe.
  • the purge assembly was then reconnected, and the He flow wasswitched from the reference purge tube 388 to the sample purge tube 387 using the dual, three-way valve system.
  • the acidified standard solution was purged for approximately 70 seconds.
  • a 0.1-mL aliquot of the saturated KMnO 4 solution was injected through the septum 381 and into the sample chamber using a syringe.
  • the chlorine gas produced from the resulting oxidation of the aqueous chloride in the sample was liberated from the solution and introduced into the flame where it formed vibrationally excited HCl. After the resulting HCl infrared emission peak had been recorded, the He flow wasswitched back through the reference purge device. Thesample purge tube 387 was then disconnected and rinsed thoroughly with deionized water to remove excess reagents. This process was repeated for all chloride standards to construct a calibration curve of peak mstensity versus chloride concentration.
  • the flame infrared emission detection system used in this experiment for the determination of chloride and available chlorine is similar to the system which has been previously described for use in total inorganic carbon (TIC) determinations in Kubala et al., Anal. Chem., 1989, Vol. 61, pgs. 1841-1846.
  • TIC total inorganic carbon
  • Figure 39A is a transmissionspectrum of the bandpass filter used in the flame infrared emission detector (maximum
  • Figure 39B is a flame infrared emissionspectrum from a
  • Figure 39C is a flame infrared emission spectrum from a hydrogen/entrained-air flame in the absence of
  • the detector bias voltage was increased from 30 V to
  • the purging apparatus ( Figure 38) consisted of twoseparate chambers, one forsample introduction and chlorine generation, and a second which served as a reference. Two, three-way valves permitted the He purge gas flow to be switched from one chamber to the other between sample
  • the flame infrared emission-Cl procedure employed a dry reference purge tube 388.
  • the flame infrared emission system functions as a mass flow-rate detector asshown in Experiment 2 .
  • the intensity of thesignal arising from the vibrational excitation of HCl in the hydrogen flame is a function of both the He flow rate and hydrogen/air ratio.
  • higher He flow rates resulted in increased peak heights and therefore increased signal-to-noise ratios, a practical upper limit was reached when the sample was forced out of the purge tube.
  • He flow rate of 130 mL/min was determined to represent the best compromise condition for maximizingsignal-to-noise ratio without sample loss.
  • H 2 + Cl 2 2HCl a fuel-rich flame was expected to enhance HCl emission and improve detection limits. As anticipated, a pure H 2 flame, supported only by entrained air, afforded SNR's that were approximately 2.5 times greater than those obtained under fuel-lean flame conditions.
  • the chloride ion must first be oxidized to chlorine gas in the sample chamber.
  • the oxidizing agent must meet two basic reguirements. First, it must have a reduction half-cell potentialsufficient to oxidize
  • the total time required for signal acquisition from an aqueous sample was approximately 3.5 min (from initial acid injection to purge tube disconnection and clean-up).
  • the hydrogen chloride signal profiles shown in Figure 40A were obtained by treatment of an acidified 1.0 ml aliquot of 8.00 mM NaCl solution with saturated KMnO 4 and those shown in Figure 40B were obtained by the addition of concentrated surfuric acid to a 0.1 ml aliquot of acidified bleach sample, diluted 20-fold (4.0 umoles available chlorine).
  • Natural water and oil brine samples were used to evaluate the analytical performance of the flame infrared emission-chlorine system for the determination of aqueous chloride.
  • the natural water samples included tap water from the Texas cities of Waco and Hewitt, surface waters from Lake
  • Table V compares the chloride values determined by argentometric titration using potassium chromate as an
  • argentometric titration may be indicative of interference from such ions as phosphate which are present in these surface waters. From Table V, the average percent relative difference for thesevensamples is 5.43%. The agreement between the results obtained with the flame infrared emission detector and the titration method is very good, considering that the titration method is not totally error free. Three commercial bleach products were used to test the performance of the flame infrared emission system for the determination of available chlorine. Bleachsamples were diluted 20-fold to give a concentration within the linear range of the flame infrared emission calibration curve.
  • Table VI compares the results obtained for available chlorine by iodometric titration with those
  • Spectral interferences in the flame infrared emission detector will occur whenever purgeable contaminants present in thesample are capable of existing as stable molecules or fragments at flame temperatures and emitting infrared radiation within the bandpass of the filter. Because of the specificity of infrared emission and the judicious selection of notch filters, however, the chance of severe interference (i.e., direct overlap) is not
  • a more subtle form of spectral interference can result from filter imperfections (or filter bleed).
  • Interference filters of the type used in the flame infrared emission-chlorine analyzer have a small, but finite,
  • the filter used in this study had a 0.1% transmittance in the vicinity of the 4.42 ⁇ m CO 2 emission band. While this transmittance seems small, optical leakage of the CO 2 band can produce measureable signals in the presence of large amounts of carbon-containing interferents.
  • Chemical interferences can occur with the flame infrared emission-chlorine analyzer in a number of ways, such as altering the oxidation process (in the case of chloride)
  • any concomitant which produces a volatile chlorine-containing compound that either does not burn readily in the flame or does not form HCl as a combustion product will depress the signal.
  • Chemical interference can also occur if a non-volatile chlorine-containing compound is produced instead of Cl 2 or if a purgeable contaminant reacts with Cl 2 in the purge gas stream and reduces the amount of
  • Bromide, iodide, and phosphate can introduce positive errors in the determination of chloride ion by argentometric titration. Since these anions can be present in natural waters at concentrations as high 1 mg/L [Br], 0.1 mg/L [I], and 0.4 mg/L [P] (Standard Methods for the
  • chloride determinations were repeated using 5mM NaCl standards which had been spiked with bromide, iodide, and phophate significantly greater than the maximum concentration expected for natural waters. The signals obtained from the spiked solutions were then compared to an unspiked 5mM NaCl standard.
  • Table VII shows that the presence of bromide, iodide, or phosphate resulted in a large positive error in the argentometric titration method, with the apparent
  • chloride concentration being given by the sum of the true chloride concentration (175 ppm) and the concentration of the interfering anion, expressed at its chloride equivalent
  • bromide can be oxidized to both Br 2 and BrO- 3 . While bromate would remain in solution, any elemental bromine would be expelled along with elemental chlorine during the purging process.
  • One method of dealing with bromide interference in the determination of chloride by argentometric procedures is to pretreat the sample using iodate ion in acid solution.
  • the flame infrared emission-chlorine procedure is capable of detecting available
  • Cl 2 in aqueous samples Since many municipalities add Cl 2 or a chlorine-containing compound (chloroamines) to tap water for disinfection, available chlorine may interfere in the determination of aqueous chloride. Thus, the initial purging step of the acid/sample mixture before oxidation of the aqueous chloride is useful in removing any available Cl 2 that may be present in the watersample.
  • Cl 2 or a chlorine-containing compound chloroamines
  • Carbon dioxide can be present in the flame as a result of purging CO 2 from an acidified carbonate-containing solution as in Kubala, et al. Anal. Chem., 1989, Vol 61. pgs.
  • Permanganate is not a sufficiently strong reagent to oxidize the majority of organic compounds to CO 2 , and with the exception of a few species such as oxalates and oxalic acids, non-volatile inorganic or organicspecies are not expected to produce a chemical interference of this type.
  • the flame infrared emission detection system is the flame infrared emission detection system
  • a special advantage of the flame infrared emission method is its lack of interference from iodide and phosphate, two ions which cause lar ⁇ e positive errors in the determination of chloride by argentometric titration.
  • the interference caused by bromide ion in the flame infrared emission method should be eliminated bysample pretreatment using iodate.
  • the schematic layout for the dual channel flame infrared emission detector is shown in Figure 42.
  • the detection system consists of an optical dual channel module, followed by the electronic signal processing module.
  • the dual channel optical arrangement is made up of a flame excitation source 421 (Hydrogen/air combustion flame), collimating lens 422, focusing lenses 423 and
  • the light from the source 421 is collimated by a calcium fluoride lens 422 of focal length 5 cm (P# 43150
  • the collimated radiation is then modulated at a frequency of 570 Hz by a mechanical light beam chopper 427
  • the modulated radiation is then passed through a zinc selenide beam splitter 426 (P#45360- Oriel corporation- Stratford - CT), which serves the role of a beams plitter dividing the radiation in two portions. Each portion of the divided radiation is then focussed onto a 1X5 mm lead selenide detector 429 (P# P791- Hamamatsu Corporation- Bridge water-
  • Optical band pass filters 428 were placed in front of the detectors fcr isolating the spectral bands of interest.
  • the filters 428 used were (1) 3.0 ⁇ 0.03 ⁇ m narrow band pass filter (P# 58160- Oriel corporation-Stratford - CT), (2) 4.4 ⁇ 0.03 ⁇ m narrow band pass filter (P# 58300- Oriel corporation- Stratford - CT), (3) 3.8 ⁇ 0.03 ⁇ m narrow band pass filter (P# 58230 - Oriel corporation- Stratford - CT), (4) 2.35 ⁇
  • One half of the divided optical path serves as the reference channel for monitoring the source background fluctuations, and the other half as the analytical channel for monitoring the analytical signals of interest.
  • the 3.0 ⁇ m filter was placed in the reference channel to monitor and compensate for the background fluctuations in the flame due to H 2 O emission from the flame. Tapending on the desired analyte, the 4.4 ⁇ m notch filter (to isolate the CO 2 emission band), the 3.8 ⁇ m notch filter (to isolate the HCl band), or 2.35 ⁇ m notch filter in combination with the 2.5 ⁇ m short pass filter (to isolate the HF band) could be placed in the analytical channel. The additional short pass filter was necessary, to effectively isolate the HF band from the strong interference band at 3.0 um due to background emission from H 2 O present in the flame.
  • the pre-amplifier circuit configuration for the dual channel system is shown in Figure 43.
  • the lead selenide detectors 431 and 432 were biased at +70 volts from a
  • the detector 431 constitute the reference arm of the wheatstone bridge network.
  • the potentionmeter 433 was used to fine tune the zero adjustment of the Wheatstone bridge to achieve an accurate balance condition.
  • the voltages, V Ri and V Ai are the voltages, V Ri and V Ai
  • the pre-amplifier circuit configuration of the reference and analytical channels are identical in all respects (in terms of the values of the resistor and capacitors, and the
  • a BIFET operational amplifier (TL 071-Texas instruments - Dallas- TX) was used.
  • the differential imput mode (A-B) of the lock-in amplifier was chosen for operation. Under these conditions the output of the lock-in amplifier is also the differential output, i.e. V AO -V RO .
  • analytical channel (with the appropriate band pass filter in place) was connected to the A input of the lock in amplifier which was operated in the single ended input mode. After proper phase setting and time constant adjustment, the approximate value of the signal was recorded.
  • the analytical channel signal was disconnected from the lock in amplifier input and the reference channel signal was connected.
  • the reference channel signal level was approximately 50 times greater than the analytical channel signal level.
  • the signal level to the reference channel was attenuated optically with an iris diaphragm 420 placed in front of the lens 424. The aperture width of the iris was adjusted until the signal level in the reference channel was approximately the same as in the analytical channel.
  • the analytical channel signal was then re-connected back to the A input of the lock-in
  • interface tube was wrapped with a heating tape and the temperature of the heating tape was maintained at 250° C.
  • the capillary burner head supported a hydrogen-air combustion flame.
  • the H 2 and the air flow rates to the burner were regulated by means of standard flow meters (P# 3227-20 (for hydrogen) and P#
  • Fluorocol. (P# 1-2425 - Supelco Inc- Bellafonte -PA). This column is specially designed for separation of fluoro and chloro carbons. Helium was used as the carrier gas through out and a flow rate of 30 mL/min was used. The liquid samples were introduced into the gas chromatograph by means of standard Hamilton microliter syringes. All the optical components were mounted on aluminum blocks designed and machined locally. The aluminum mounts were painted flat black to minimize stray radiation and reflections reaching the detector. A shield made of aluminum and painted flat black on both the inside and the outside was placed around the burner to minimize flame flicker due to air currents from the atmosphere and the chopper blade. All experiments were performed after a 30 minute warm-up period to allow for the stabilization of electronic components and leadselenide detector response.
  • anyselective detection system since a given selective detection system should have a high selectivity towards a species of interest and at the same time should be able to detect very small quantities of that species.
  • the experimental variables that were considered to have a significant effect on these two parameters were (a) detector bias voltage (b) the optical filter in the reference channel for background compensation and (c) the method of balancing the Wheatstone bridge network.
  • Freon-113 was used to evaluate the response of the system in the fluorine, and chlorine selective modes of operation.
  • Pentane was used as the hydrocarbon comparison standard for evaluation of
  • V volume (mL) injected and d is density (g/mL).
  • the selectivity ratio is the ratio of the signal for
  • Freon-113 shows a distinct minimum around 70 volts, and a further increase in the bias voltage leads to poorer
  • the Wheatstone bridge network used for the optical attenuation method is shown in Figure 43. This method has already been discussed. The bridge balance condition was achieved (under the flame background conditions) by optically attenuating the signal intensity in the reference channel by means of an iris diaphragm, until it approximately equaled the signal in the analytical channel. Under these conditions any fluctuations in source intensity common to both channels would mutually cancel each other and onlysignals due to species of interest would appear in the analytical channel.
  • the electronic attentuation method could further be classified into (1) an adjustable load resistor method and (2) an adjustable pre amplifier gain method.
  • the Wheatstone bridge network used in the adjustable load resistor method is shown in Figure 45.
  • the bridge balance (under the flame background conditions) was achieved by adjusting the value of the resistance of the load resistor 451 on the reference arm of the bridge.
  • the load resistor 451 and the lead selenide detector 453 constitute the reference arm of the wheatstone bridge.
  • the load resistor 451 on the reference channel is a multiturn trimmer potentionmeter whose value could be
  • the Wheatstone bridge network used in the adjustable pre-amplifier gain method is shown in Figure 46. It is essentially the same as used in the previous method, shown in
  • V Ao and V Ro are made equal by adjusting the gain of the reference preamplifier circuit with a gain control resistor 465.
  • the gain of the reference channel circuit was adjusted until the signal level V RO became equal to V AO . Under these condition the differential output (V AO -V RO ) is zero.
  • Table XIV summarizes the relative performance of the dual channel system in the subtracted mode to that of the unsubtracted mode obtained under the optimum conditions mentioned above .
  • the detection limit for pentane and for Freon-113 are about the same. However, in the unsubtracted mode, the detection limit for pentane is about an order of magnitude better than that for Freon-113.
  • concentration range from 0.1 to 10 micrograms.
  • the calibration plots indicate excellent linearity in the detector response for the amounts of Freon-113 injected.
  • chlorofluorocarbon mixture was chosen for this purpose.
  • the essential idea behind this approach was that in a mixture of chlorofluorocarbon and hydrocarbons chromatographed under an element selective mode, only the compounds containing the given element of interest would respond while others would be virtually excluded.
  • a synthetic mixture ofseven compounds consisting of chlorinated, fluorinated and aliphatic
  • hydrocarbons was prepared.
  • the composition of this mixture and the chromatographic conditions are given below.
  • the chlorine selective mode was carried out using the 3. 8 ⁇ m filter in the analytical channel.
  • the carbon mode of operation was carried out using the 4.4 ⁇ m filter in the analytical channel.
  • a 3.0 um filter was used throughout in the reference channel. All chromatograms were run under identical
  • the fluorine selective GC-flame infrared emission detector provides the ideal choice. Since the fluorine selective mode of the detector responds selectively only to the fluorinated compounds, a simpler chromatograph with less peaks results, obviating the need for tedious and elaborate optimization schemes. Unambiguous qualitiative identification and reliable quantitative data can be achieved under these conditions. As a part of our investigative study of the performance of the dual channel system operating in the fluorine selective mode, we have attempted to simulatesuch a condition; the details of the experimental approach are descibed in the following section.
  • a complex 19-component mixture of various organic compounds was prepared by mixing these compounds in
  • composition of this mixture is given below.
  • Carbopack-B (5%Fluorocol), helium carrier gas (30 mL/min), temperature programming 180°C to 220°C at 20°C/min.
  • the 19 component complex mixture was chromatographed under these conditions, with (a) a commercial TCD detector, (b) a flame infrared emission detector in the carbon mode and (c) a flame infrared emission detector in the fluorine selective mode.
  • the chromatograms for the respective modes areshown in
  • a flame infrared emission detector is combined with a flame ionization detector wherein thesame flame is used tosimultaneously conduct both types of detection.
  • the flame infrared detector provides better quantitation of moles of carbon present in the compounds while the flame ionization detector provides higher
  • the flame infrared emission detector is able to detect compounds not observed by the flame ionization
  • FIG. 52 An experimental schematic for a combined flame infrared emission flame ionization detector is shown in Figure 52.
  • the burner body 520 is thesame as used for Experiment 2.
  • Hydrogen/Air is used as the fuel/oxidant mixture being supplied to the capillary tubes of the burner through a Swagelok T 523a, 523b.
  • the sample is supplied through the central capillary 526.
  • the flame ionization detector utilizes two electrodes in an electrode assembly 522 where a potential of
  • the infrared emission is simultaneously detected by a PbSe detector 524. Radiation from the flame is modulated by an optical chopper 525. The infrared detector 524 must not "see” the electrodes (due to blackbody emission
  • an aperture device is mounted on the infrared detector unit.

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Abstract

L'appareil et le procédé d'observation d'émission infrarouge provenant de molecules excitées se trouvant dans des échantillons d'intérêt ont étés étudiés. Sur l'intervalle de longueur d'onde compris entre 1 et 5 νm, on a observé deux bandes d'émission fortes à l'aide d'un détecteur PbSe (429), lorsque l'on a introduit des composés organiques dans une flamme d'hydrogène/air (421). La bande à 4,3 νm (2326cm-1) est due à l'étirement asymétrique de dioxyde de carbone, tandis que la bande à 2,7 νm est due à l'émission à la fois d'eau et de dioxyde de carbone. On a découvert que l'émission de dioxyde de carbone à 4,3 νm atteint son intensité la plus élevée à la pointe de la flamme (421), et qu'elle augmente avec la quantité de composé organique introduit dans la flamme (421). Pour une application chromatographique, on a utilisé un filtre optique (428) afin d'isoler la bande d'émission de 4,3 νm. Le système de détection d'émission infrarouge trouve une application dans la détermination de la quantité totale de carbone inorganique, de chlorure et de chlore disponible dans des échantillons aqueux. Le détecteur est optimisé par l'emploi d'un système à double vaisseau capable de soustraire le fond, éliminant ainsi le bruit de fond ainsi que ses fluctuations.
PCT/US1990/005591 1989-09-29 1990-10-01 Detection d'emission infrarouge Ceased WO1991005241A1 (fr)

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US415,141 1989-09-29
US07/415,141 US5246868A (en) 1987-10-26 1989-09-29 Infrared emission detection

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Cited By (7)

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Publication number Priority date Publication date Assignee Title
DE4231777A1 (de) * 1992-09-23 1994-03-24 Fraunhofer Ges Forschung Verfahren zur spektralen Analyse von technischen Flammen durch optische Emissionsmessung und Anordnung hierfür
US5473162A (en) * 1987-10-26 1995-12-05 Baylor University Infrared emission detection of a gas
WO1999050649A1 (fr) * 1998-03-27 1999-10-07 The Secretary Of State For Defence Detecteur a photometrie de flamme
FR2799838A1 (fr) * 1999-10-18 2001-04-20 Centre Nat Rech Scient Procede d'analyse et de dosage d'elements legers et appareillage pour sa mise en oeuvre
US9194274B2 (en) 2010-08-06 2015-11-24 Avl Test Systems, Inc. Particulate measurement system
CN109300564A (zh) * 2018-09-20 2019-02-01 中国辐射防护研究院 一种模拟蒸汽堵塞和腐蚀过滤器的装置和方法
CN115791681A (zh) * 2022-11-09 2023-03-14 招商局重庆交通科研设计院有限公司 沥青质量管控方法及系统

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US3871768A (en) * 1972-08-24 1975-03-18 Ronald Belcher Molecular emission cavity analysis
US4249168A (en) * 1978-04-25 1981-02-03 Cerberus Ag Flame detector
US4311485A (en) * 1980-12-23 1982-01-19 E. I. Du Pont De Nemours And Company Method and apparatus for photometrically monitoring the concentrations of both chlorine and chlorine dioxide
US4466943A (en) * 1979-11-28 1984-08-21 Nissan Motor Co., Ltd. Flame photometric detector analyzer

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US3723831A (en) * 1970-12-04 1973-03-27 Arco Corp Indium antimonide infrared ray detector
US3871768A (en) * 1972-08-24 1975-03-18 Ronald Belcher Molecular emission cavity analysis
US4249168A (en) * 1978-04-25 1981-02-03 Cerberus Ag Flame detector
US4466943A (en) * 1979-11-28 1984-08-21 Nissan Motor Co., Ltd. Flame photometric detector analyzer
US4311485A (en) * 1980-12-23 1982-01-19 E. I. Du Pont De Nemours And Company Method and apparatus for photometrically monitoring the concentrations of both chlorine and chlorine dioxide

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See also references of EP0494266A4 *

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5473162A (en) * 1987-10-26 1995-12-05 Baylor University Infrared emission detection of a gas
DE4231777A1 (de) * 1992-09-23 1994-03-24 Fraunhofer Ges Forschung Verfahren zur spektralen Analyse von technischen Flammen durch optische Emissionsmessung und Anordnung hierfür
WO1994008228A1 (fr) * 1992-09-23 1994-04-14 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Procede et dispositif d'analyse spectrale de flammes industrielles par mesure optique des emissions
WO1999050649A1 (fr) * 1998-03-27 1999-10-07 The Secretary Of State For Defence Detecteur a photometrie de flamme
GB2352034A (en) * 1998-03-27 2001-01-17 Secr Defence Flame photometer detector
GB2352034B (en) * 1998-03-27 2002-09-25 Secr Defence Flame photometer detector
FR2799838A1 (fr) * 1999-10-18 2001-04-20 Centre Nat Rech Scient Procede d'analyse et de dosage d'elements legers et appareillage pour sa mise en oeuvre
WO2001029540A1 (fr) * 1999-10-18 2001-04-26 Centre National De La Recherche Scientifique Procede d'analyse et de dosage d'elements legers et appareillage pour sa mise en oeuvre
US9194274B2 (en) 2010-08-06 2015-11-24 Avl Test Systems, Inc. Particulate measurement system
CN109300564A (zh) * 2018-09-20 2019-02-01 中国辐射防护研究院 一种模拟蒸汽堵塞和腐蚀过滤器的装置和方法
CN109300564B (zh) * 2018-09-20 2022-11-18 中国辐射防护研究院 一种模拟蒸汽堵塞和腐蚀过滤器的装置和方法
CN115791681A (zh) * 2022-11-09 2023-03-14 招商局重庆交通科研设计院有限公司 沥青质量管控方法及系统

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CA2026613A1 (fr) 1991-03-30
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EP0494266A4 (en) 1992-12-09

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