SU1160297A1 - Gas chromatograph - Google Patents

Description

The invention relates to gas chromatographs, designed primarily for the analysis of impurities of light gases in various gas mixtures. five

Light gases in chromatography refer to hydrogen, oxygen, nitrogen, elements of the zero group of the periodic table, and other gases, characterized, as a rule, by short retention times in the chromatographic column. Since a heat conduction detector (catarometer) 15 of a flow type is usually used as a detector in the analysis of light gas impurities, it is more sensitive to fluctuations of parameters (flow rate, pressure) of gas flows.

ι A gas chromatograph is known, which contains a series-connected gas pressure regulator, a controlled valve, a sample dispenser, the first and second chromatographic columns, and a detector. An additional carrier gas line with a pressure regulator and a controllable valve is connected to the line between the first and second chromatographic columns. The chromatograph also contains waste lines with controlled valves and pneumatic chokes, connected to the sample dispenser and to the output of the first chromatographic column [Ύ3 ·

The disadvantage of this chromatograph 35 is its complexity, caused by the large number of locking regulatory elements in the circuit. In addition, the lack of a chromatograph is also the fact that it does not eliminate ⁴⁰ fluctuations of the carrier gas flow pressure during sample dosing. Depending on the way the sample is introduced, the nature of the disturbances introduced by the dispenser into the carrier gas stream may be different · ⁴ ^. If the sample is injected into the flow with a syringe dispenser, it creates an excess pressure with respect to the flow. If the dosing is carried out using a crane with a 5 ° sampling loop, the nature of the pressure push depends on the pressure under which the sample in the loop is in the loop in relation to the flow of carrier gas, 55 introduced by the dosing operation into the gas flow, manifested in the output signal of the detector at the time of the appearance of the useful signal and superimposed on it, introducing a significant error in the analysis results ·. In the analysis of impurities of light gases with. the concentration in the mixture of the order of tenths and hundredths of a percent of the chromatographic peak can be completely covered by the peak of the disturbance signal, which leads to unreliable results or eliminates the possibility of analyzing such mixtures without enriching the sample.

The closest in technical essence to the invention is a gas chromatograph containing a carrier gas flow regulator connected in series, a sample dispenser in the form of a switching valve. With a sampling gauge. boron loop, column, detector and bypass gas line with a throttle connected to the output of the flow regulator and the input of the column [2],

In the well-known chromatograph solved the problem of programming the gas flow rate in the chromatographic column while maintaining a constant velocity of the carrier gas flowing through the detector. However, it has a number of drawbacks, one of which is the large error in the analysis due to the varying degree of dilution of the sample with the carrier gas coming to the detector input via a bypass line and ι mixing with the gas flow, “And the chromatograph does not take into account the fact that the chromatographic column, especially packed type, changes with time, which leads to uncontrolled redistribution of gas flows in the column and the bypass line, as a result, to an additional error of analysis. Regardless of the way the sample is introduced (the sample dispenser type is not specified), the well-known chromatograph also does not solve the problem of eliminating pressure fluctuations in the gas flow entering the detector, caused both by the operation of the regulators installed at the inlet of the column and bypass, and when the dispenser is injected. The pressure regulator installed at the outlet of the chromatographic column is also an additional source of error, since it has stagnant zones where part of the analyzed pbbg can be lost. Taken together, these 'drawbacks of the scheme of a known chromatograph lead to an ana3 error

Lysis of light gases within 1ΟΣΟ rel. at their concentration in mixtures of the order of a few percent or makes it impossible to analyze mixtures with a concentration of light gases of 10 ~ ¹ 10-2 OBD.

The purpose of the invention is to improve the accuracy of the analysis of light gases by eliminating pressure shocks when dosing samples and reducing the degree of dilution of the sample with a carrier gas.

This goal is achieved by the fact that in a gas chromatograph containing serially connected a 15 gas flow controller, a sample dispenser in the form of a switching valve with a sampling loop, a chromatographic column, a detector and a bypass gas line with a throttle connected to the output of the control panel flow rate and the input of the column, at the entrance to the sample dispenser after the point of connection of the bypass line, a controlled shut-off valve is installed, an additional bypass line 25 with throttle is connected, connected at one end to the output from the flow controller, and the other end through the switching valve - to the inlet of the chromatographic column that is connected to the other end of the main bypass line "

The choke resistance of the additional bypass line may be

equal to sampling resistance

. '<·. 35

loops.

FIG. 1-3 shows the design of the scheme with a sample dispenser in the form of a so-called tap dispenser, in which

Sampling loop in process for * - 40

the filling of the analyte is completely isolated from the carrier gas stream; figure 4 is a variant of the scheme "beskranovogo" input samples in the chromatographic column, allowing you to display the switching valve dispenser ⁴⁵ samples outside the thermostat; FIG. 5 is a variant of a chromatographic scheme in which a sample can be introduced with a syringe.

' 50

The proposed gas chromatograph (figure 1) contains a series-connected regulator 1 of the flow rate of the carrier gas, consisting, for example, of the regulator 2 pressure and throttle 3, 55

Dispenser 4 samples in the form of a switching valve 5 with a sampling loop 6, chromatographic column 7 and detectors 1160297 *

torus 8. A bypass line 9 is connected to the output of the flow regulator 1 with a throttle 10, the output of which is connected to the input of the chromatographic column 7. A shutoff valve 11 is installed on the carrier gas line before entering the 4 sample dispenser, and an additional bypass line 12 with 10 choke 13.

In another embodiment (FIG. 4), the chromatograph contains a regulator 14 of the pressure of the gas to be analyzed and a choke 15 installed at the outlet of the sample dispenser.

According to the third variant (FIG. 5), the chromatograph contains a device 16 for inserting a needle of a syringe into a sampling loop. ►

The proposed gas chromatograph works as follows.

In the first cycle (FIG. 1), the sampling loop 6 of the dispenser 4 is filled with the analyzed gas. In this case, the valve 11 blocks the flow of the gas carrier, which, bypassing the sampling loop 6, passes through the bypass lines 9 and 12 through the throttles 10 and 13 to the input of the chromatographic column 7 and then to the detector 8.

In the second cycle (figure 2) switch the valve 5, informing the sampling loop with the outlet of the valve 11 and the column

7. When this occurs, the pressure in the gas line in front of the column and in the sampling loop is equalized 6. The process of pressure equalization is recorded by the detector 8 and recorded as a peak on the tape recorder (not shown).

At the end of the transition process, the pressure equalization of the valve 11 is transferred to the open position (FIG. 3). At the same time, the sample of the analyzed gas is displaced by a flow of carrier gas from the sampling loop 6 to the chromatographic column 7, where the components of the Mixture are separated, which then go to the detector 8.

The presence of the bypass line 9 with the throttle 10 eliminates the interruption of the gas flow in the measuring chamber of the detector 8. With the help of the bypass line 12 and the throttle 13, the resistance of which is equal to the resistance of the sampling loop 6, the parameters of the gas flow are constant (1160297)

tector 8 regardless of the positions of the switching valve 5 and valve 1G.

Thus, the introduction of a controlled shut-off valve 11 and an additional 5 bypass line 12 with throttle 13 into the chromatograph system eliminates the appearance of false peaks on the chromatogram associated with the instability of pressures and flow rates of gas streams when they are switched, and also divide the measurement signals of the detector and Signals due to pressure changes as the sample is injected. This makes it possible to significantly improve the accuracy of chromatograph measurements, especially when analyzing light gases with their concentration in mixtures at the Level of hundredths of a percent or less.

According to experimental data, the error in the analysis of light gas impurities 20. (For example, with the concentration of hydrogen and oxygen in mixtures at levels of 10 ″ ² - 10 ’ ³ v L, the proposed chromatograph with a thermal conductivity detector is reduced compared to 25 with the known 4–5 times.

A significant advantage of the proposed chromatograph in comparison with the known one is that it allows one to take a sample here both under pressure

and under vacuum, which is especially important when using the chromatograph in the control of environmental pollution, or when sampling from objects under reduced pressure. The proposed chromatograph allows the use of all known systems for the selection and input of the sample. For example, in the “crane-free” sample input (FIG. 4) using the control shut-off valve and an additional bypass, the same positive effect is achieved as in the first embodiment. The circuit operation (FIG. 4) is similar to the operation of the described variant. The difference of the circuit itself is that the analyzed gas in the sampling loop when sampling is isolated from the carrier gas flow by means of the throttle 15, on both sides of which create the same pressure of gas flows. The specified pressure level from the analyzed gas is maintained Knob 14 pressure.

The difference in the scheme of the third variant (figure 5) from the first is only the connection to the sampling loop (devices for inserting the needle of the syringe 16 for those cases when the sample is introduced into the system manually ..

1160297

FIG. 3

Carrier gas

Analyzed gas

FIG. four

(160297

Claims (2)

1. GAS CHROMATOGRAPH containing serially connected regulator of carrier gas flow rate, sample dispenser, in the form of a switching valve with a sampling loop, chromatographic column, detector and bypass gas line with throttle, connected to the output of the flow regulator and the inlet of the column, characterized in that, in order to improve the accuracy of light gas analysis by reducing pressure shocks when dosing samples, a controlled shut-off valve is installed at the inlet to the sample dispenser after the bypass line and an additional bypass line with throttle connected at one end to the output of the flow regulator and at the other end through a switching valve to the input of the chromatographic column to which the other end of the main bypass is connected ii. 2. Chromatograph on π. 1, the fact that the resistance of the additional bypass line is chosen equal to the resistance of the sample loop breakdown. „., 511„ 1160297 1 1 1160297 2