RU2571451C1 - Gas microchromatograph for analysis of organic and inorganic substances - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: gas microchromatograph for analysis of organic and inorganic substances contains source of carrier gas, two microbatcher on flat plates, capillary column and planar microchromatographic column with two microdetectros on output. It also contains low-inertial heat-conductivity detector HCD and thermochemical detector MTCD with sensitive elements, placed in one flow chamber, and device for obtaining calibration mixtures. Device for obtaining calibration mixtures contains thermostatable tubular flow system, filled with granular sorbent, which consists of three sections, first of which is connected with carrier gas source, and third section by means of switch valve is connected to input of microbatchers instead of analysed mixture line.

EFFECT: increased correctness of measurement of analysed component concentration, increased precision of measuring height and area of chromatographic peaks, as well as reduction of error of measuring analysed component concentration when parameters of chromatographic process change.

1 dwg, 1 tbl

Description

The invention relates to gas chromatography and can be used for the quantitative analysis of complex mixtures of organic and inorganic substances of natural and technogenic origin in various industries: chemical, petroleum, petrochemical, energy, medicine, biology, ecology, etc.

Known capillary gas chromatographs with a flame ionization detector (PID) for efficient and rapid separation of complex mixtures of organic substances (see: High-performance gas chromatography / Edited by K. Heifer. M .: Mir, 1993, 288 p.).

The disadvantage of capillary chromatographs is the inability to analyze inorganic substances, since the FID registers only organic substances.

Existing gas chromatographs provide high accuracy and reliability of the analysis, however, they are not without such drawbacks as cumbersomeness, high cost and certain difficulties in operation.

A pronounced trend in the development of modern analytical instrumentation is the miniaturization of equipment in order to conduct specific types of analysis. The advantages of microdevices include the small size, weight, speed of analysis (see: Microfluidic systems for chemical analysis / Edited by Zolotov Yu.A., Kurochkina V.E.M .: Fizmatizdat, 2011, 528 p.).

Portable and portable gas chromatographs are also known, the main units and blocks of which are made using new advances in microelectronics and micromechanics of MEMS technology (see: Yashin Y.I., Yashin S.Ya., Yashin A.Ya. Gas chromatography. M: Publishing house "Trans-Lit", 2009, S. 384-401).

However, the known portable and portable gas chromatographs produced by foreign and domestic manufacturers for a specific analytical task are not equipped with additional devices for metrological support, for example, a device for producing calibration mixtures.

A known method and device for producing calibration mixtures of volatile components, in which the inert gas stream is continuously in contact with the granular layer of the stationary phase, consisting of a low-volatile liquid deposited on the particles of the solid carrier, and the stationary phase is saturated with vapor of volatile components to equilibrium concentrations at the inlet and outlet of the tubular flow system at temperatures exceeding operating temperatures corresponding to constant concentrations of volatile components for calibration mixtures various composition. Moreover, the tubular flow system is made of at least three series-connected sections, the first of which has a greater percentage of impregnation of the solid carrier with a low-volatile liquid compared to the subsequent ones. A calibration mixture with a calculated concentration of volatile components in an inert gas stream is selected from the third section (RF Patent No. 224173. IPC G01N 30/06, published May 10, 2008).

Also known is a low-inertia thermal conductivity detector for gas chromatography, comprising a heater made in the form of a metal thread, two film thermosensitive elements installed in the gas channel at the outlet of the capillary column parallel to this heater at the same distance from it and included in the opposite shoulders of the bridge measuring circuit, and the power source for heating the heater contains an autoregulator that keeps its temperature and resistance constant (RF Patent No. 2266534, PC G01N 30/61, publ. December 20, 2005).

However, the known devices for producing calibration mixtures and a low inertia thermal conductivity detector for capillary chromatography are not included in the commercially available capillary gas chromatographs.

Closest to the invention in terms of essential features is a capillary gas chromatograph for the analysis of organic and inorganic substances, containing a carrier gas source, two metering valves, a capillary column, a device for producing calibration mixtures and a low-inertia detector for thermal conductivity (RF Patent. No. 2302630 IPC G01N 30 / 02, published July 10, 2007).

A disadvantage of the known capillary gas chromatograph is the absence in its description of constructive solutions for individual units and devices that determine the accuracy and precision of the measurement of the main chromatographic characteristics, including:

- a planar microdoser for direct injection of the sample into capillary or micropacking columns without dividing the flow;

- planar microchromatographic column;

- the use of a two-channel system for the analysis of complex mixtures of organic and inorganic substances.

The objective of the invention is to improve the accuracy and precision of the measurement of basic chromatographic characteristics.

This problem is solved due to the fact that in a gas microchromatograph for the analysis of organic and inorganic substances containing a source of carrier gas, two metering valves with fixed volumes of doses, a capillary column with a low-inertia detector for thermal conductivity at the outlet, a switch valve and a device for producing calibration mixtures, additionally contains a planar microchromatographic column made on a flat plate, for example, of aluminum by laser ablation with a microthermochemical detector on a course that has two heat-sensitive elements in the form of platinum threads included in the bridge measurement circuit and placed in one flow chamber, and the working thread is covered with a thin film of a catalyst for the oxidation of organic compounds, the input of each column being connected to the outlet of one of the metering valves made together with doses on flat aluminum plates by microfilling for direct injection of the sample without dividing the flow, and the device for producing calibration mixtures contains a thermostatically controlled tubular a flow system filled with a granular sorbent, consisting of three successively connected sections with the same dimensions, the first of which is connected to a carrier gas source and has a higher percentage of impregnation of a solid carrier with a low-volatile liquid compared to the subsequent ones, the third section is connected to the input using a switching tap dosing valves instead of the line of the analyzed mixture.

When solving this problem, a technical result is created, which consists in the following:

1. The use in the proposed gas microchromatograph of a new device for producing calibration mixtures made it possible to obtain more than five multicomponent mixtures with different concentrations of the analyzed components to build calibration characteristics instead of two mixtures in the prototype, which increased the accuracy of measuring the concentrations of the analyzed components.

2. The implementation of metering valves with a fixed volume of doses on flat plates by microfilling for direct injection of the sample into capillary and micro-nozzle columns without dividing the flow can improve the precision of measuring the height and area of chromatographic peaks.

3. The manufacture of a planar microchromatographic column on a flat plate by laser ablation increases the precision of measuring retention time, separation factor, height of the equivalent theoretical plate and other chromatographic characteristics.

4. The use of a microthermochemical detector for the analysis of organic substances can significantly reduce the error in measuring the concentration of the analyzed components when changing the parameters of the chromatographic process, such as ambient temperature, temperature of platinum filaments and detector chambers, temperature of the gas flow entering the detector from the column, carrier gas flow at the output of the column, the voltage of the power supply of the measuring bridge of the detector, etc.

The invention is illustrated in the drawing.

The drawing schematically shows a gas microchromatograph for the analysis of organic and inorganic substances, which contains a source of carrier gases 1: helium for a channel with a low-inertia detector МДТП 7 and air for a channel with a microthermochemical detector МДТХ 9, two thermostatically controlled microdosing taps 2 and 3, made on flat micro-milling plates together with fixed doses of 4 and 5 with a volume of 50 μl, capillary column 6 for the analysis of inorganic components of the sample with a low-inertia detector MDTP 7, execution According to RF patent No. 2266534 dated December 20, 2005, a thermostatically controlled planar microchromatographic column 8 with a microthermochemical detector МТТХ 9 for analysis of organic components of a sample, a thermostatically controlled device for producing calibration mixtures 10, consisting of sections 12, 13 and 14, made according to the RF patent № 2324173 dated May 10, 2008 and a switching crane 11.

Organic gas microchromatograph

The analyzed test mixture or calibration mixture from the device 10 is supplied to doses 5 and 4 of the microdosers 3 and 2. To switch the gas flows, each microdoser is equipped with three electrically controlled pneumatic valves that are mounted on a flat plate. Directional valves have two operating positions: “electric control on” and “electric control off”.

The drawing schematically shows the position of the "set" (electric control included). In this case, the analyzed or calibration mixture is filled with doses 4 and 5 of columns 6 and 8 for chromatographic separation, as a result of which the detectors 7 and 9 record chromatograms of the analyzed components.

As the material for the creation of microdosers 2 and 3 and planar microchromatographic column 8, aluminum was chosen due to the inertness of its surface with respect to the analytes under study and the simplicity of processing when creating a channel system on the plane. The use of microchannels on the plane to create gas chromatographic columns allows us to simplify the procedure for filling the columns with sorbent and significantly reduce their cost. The plates themselves act as solid state thermostats. A polyimide film with a layer of chromium deposited on its surface is used as a heater. This technology not only facilitates the installation of thermostatically controlled chromatograph elements, but also leads to a significant reduction in the energy consumption of the device as a whole.

A device for producing calibration mixtures 10 operates as follows. The analyzed mixture is passed through a flow tube system at a temperature of 100 ° C until equilibrium concentrations are obtained at the inlet and outlet of the system or until a “breakthrough” occurs, with section 12 containing 40 wt.%, Low-volatile squalane liquid on a solid support, and sections 13 and 14 of 30 wt.%, squalane. By setting the various operating temperatures of the tubular flow system lower than the saturation temperature of the sorbent with volatile components, several calibration mixtures with different, constant in time, concentrations of these components are obtained, and the use of a larger percentage of impregnation of the solid support with squalane in the first section increases the time interval for maintaining constant concentrations of volatile components components in the inert gas stream by feeding the second and third sections of the tubular system with volatile components from first section. The resulting calibration mixtures are metered into the chromatograph instead of the analyzed mixture to build a calibration characteristic for each component.

The proposed gas microchromatograph contains a planar microchromatographic column filled with nanosized silica (Aerosil A-175), length 2 m, channel cross section 0.2 × 0.2 mm, column temperature 40 ° C, carrier gas — air, outlet flow rate 2 cm ³ / min, the MDTX detector was compared with a known chromatograph using a commercial GasPro capillary column from Agilent Technologies (30 m × 0.25 mm × 0.5 μm), the carrier gas was helium, and the outlet flow rate was 4 cm ³ / min, column temperature 80 ° C, MDTP detector. This column is a recognized leader among world analogues in the analysis of natural gas components. A grading mixture of low-boiling C ₂ -C ₅ alkanes in helium was used as an object of study.

According to the results of the experiments were calculated:

- The correct measurement of the concentration of the analyzed components, δ _i ,%

where C _{i, ref} is the initial concentration of the i-th component in the sample; C _i , _ISM is the measured concentration of the i-th component.

- The separation factor α of two adjacent components

и

- приведенные времена удерживания соседних сорбатов с меньшим и большим временем удерживания соответственно.Where

and

- reduced retention times of neighboring sorbates with shorter and longer retention times, respectively.

, %.- The standard deviation (RMS) of the area of the chromatographic peak, $${\text{S}}_{{\text{A}}_{\text{i}}}$$

,%.

- среднеарифметическое значение площади.where A _i is the area of the i-th component in the sample; n is the number of measurements, n = 10;

- arithmetic mean value of the area.

, %.- The standard deviation of the retention time $${\text{S}}_{{\text{t}}_{\text{i}}}$$

,%.

- время удерживания i-го компонента в выборке; n=10 - число измерений; $${\overline{\text{t}}}_{{\text{R}}_{\text{i}}}$$

- среднее арифметическое значение времени удерживания.Where $${\text{t}}_{{\text{R}}_{\text{i}}}$$

- retention time of the i-th component in the sample; n = 10 is the number of measurements; $${\overline{\text{t}}}_{{\text{R}}_{\text{i}}}$$

is the arithmetic mean of the retention time.

The experimental results are summarized in the table "Comparative data of the experimental verification of the known and proposed chromatographs."

As can be seen from the data in the table, the accuracy of measuring the concentration of the analyzed components is on average twice as good as the known chromatograph, which is due to the use of a new device for producing calibration mixtures and the construction of calibration characteristics of the chromatograph for each component of the analyzed mixture.

и $${\text{S}}_{{\text{t}}_{\text{i}}}$$

для предлагаемого хроматографа в пять раз лучше этих предельных значений. Прецизионность предлагаемого хроматографа повысилась за счет изготовления микродозаторов и микрохроматографических колонок на плоских пластинах, а также использования микротермохимического детектора МДТХ, обеспечивающего уменьшение влияния различных параметров хроматографического процесса на результаты измерения.When assessing the precision of measurements for known gas chromatographs equipped with a metering valve, the standard deviation was taken from the values of the peak areas and the retention time of not more than 2.0%, which are recorded in the normative and technical documentation. Measured values $${\text{S}}_{{\text{A}}_{\text{i}}}$$

and $${\text{S}}_{{\text{t}}_{\text{i}}}$$

for the proposed chromatograph is five times better than these limit values. The precision of the proposed chromatograph has increased due to the manufacture of microdosers and microchromatographic columns on flat plates, as well as the use of a microthermochemical detector MDTX, which reduces the influence of various parameters of the chromatographic process on the measurement results.

The use of the proposed gas microchromatograph for the analysis of organic and inorganic substances will contribute to the creation of metrologically sound chromatographic measurement techniques for the implementation of specific (target) analytical tasks, including rapid analysis methods with short micropackered columns of various technological objects and field analyzes with portable instrument configuration.

Claims (1)

A gas microchromatograph for analyzing organic and inorganic substances, containing a carrier gas source, two metering taps with fixed dose volumes, a capillary column with a low-inertia detector for thermal conductivity at the inlet, a switching tap and a device for producing calibration mixtures, characterized in that it further comprises a planar microchromatographic column made on a flat plate, for example, from aluminum by laser ablation with a microthermochemical detector at the output, which has thermally sensitive elements in the form of platinum threads included in the bridge measuring circuit and placed in one flow chamber, and the working thread is covered with a thin film of a catalyst for the oxidation of organic compounds, the input of each column being connected to the outlet of one of the metering valves, made together with doses on flat micron-milling aluminum plates for direct injection of the sample without dividing the flow, and the device for producing graduated mixtures contains a thermostatically controlled tubular flow system mu filled with granular sorbent consisting of three series-connected sections with the same dimensions, the first of which is connected to a source of carrier gas, and a third section by the switching tap connected to the input line instead microdispensers mixture being analyzed.