SU997766A1 - Apparatus for preparative calibration of vapour gas mixtures - Google Patents

Description

The invention relates to analytical technique, to the field of analytical *: instrumentation, specifically ”to devices for calibrating chromatographic, graphical analyzers and gas analyzers- ³ congestion.

A device is known comprising “a container with a magnetic stirrer and a piece of * frame for the entrance of carrier gas and the outlet of the gas mixture 11].

Significant disadvantages of this device are:

- the relatively low accuracy of determining metrological characteristics ~ due to the exponential nature of the change in the concentration of the analyte at the outlet of the vessel;

- distortion of the functional relationship between concentration and operating parameters due to sorption on the surface and imperfect mixing in the vessel.

The closest to the invention in terms of technical essence is a device containing a channel for supplying _e- gas - * carrier, a capillary with analyte- ²³ substance connected to a channel for supplying gas carrier, and a channel for exiting the mixture [2].

A significant disadvantage of this device is the temporary pesta-. θ concentration of the gas-vapor mixture.

The purpose of the invention is to ensure the stability of the concentration of the vapor-gas mixture by maintaining a constant level of the analyte in the capillary.

This goal is achieved in that the device for the preparation of gas-vapor calibration mixtures, containing a channel for supplying a carrier gas, a capillary partially filled with an analyte and connected to the upper end with a channel for supplying a carrier gas, is equipped with a semi-permeable membrane fixed to the lower end of the capillary, and a container with a solvent, in which the lower end of the capillary is located, and a saline solution is placed above the membrane in the capillary.

The drawing shows the proposed device.

The carrier gas stream is connected to a channel 1 connected to a capillary 2, partially filled with an analyte 3, and a channel 4 for the mixture to exit. Saline solution 5 is poured into the capillary, the lower end of the capillary is tightened with a semipermeable membrane 6 and placed in a vessel 7 with solvent 8. Channels 1 and 4 are connected by pipeline 9.

The device operates as follows.

When a capillary 2 'is immersed in a vessel 7 with a solvent 8 due to the unilateral permeability of the solvent through a semipermeable membrane 6, an osmotic pressure arises, which is described quite well by the Vant-Hoff equation for low salt concentrations: in this case, it will be determined by the difference in the specific gravities of the analyte and the saline solution.

For experimental verification of the proposed device was prepared from 5 linen layout. The capillary is made of a glass tube with an inner diameter of 2 mm. A solution of magnesium sulfate in water was used as a saline solution. The analyte is hexane. Temperature 25 ° C

P is CRT,

- salt concentration;

- universal gas constant;

T is the temperature.

Under the influence of this pressure, solvent 8 penetrates into capillary 2 until the pressure of the liquid columns in the capillary balances the osmotic pressure P, and the pressure of the liquid columns P ₂ at the bottom of the droplet * l ery 2 is determined from the relation ^ p-1- ( 3. (114+ 02.1-12,!

^h 4 d ₂

- specific gravity of the analyte;

- the height of the column of the analyte;

-specific weight of saline solution;

saline column height.

h _a

In the established equilibrium, there will be a certain length of the diffusion path from the surface of the analyzed liquid to the carrier gas stream and the concentration of the analyte to be poured where the substances in the stream can be defined by the formula c - c. C i

° LQ '

- the concentration of the analyte in the meniscus fluid; ·

- vapor diffusion coefficient in the carrier gas;

- area of the cross section of the capillary;

"· The length of the diffusion path;

- gas consumption - carrier.

L

Q . . _ ___________

As a result of evaporation of the analyte under a certain period of time, the length of the diffusion path will increase, which will lead to a decrease in the concentration of the analyte in the carrier gas stream. At the same time, the total height of the liquid columns will decrease, which will lead to an imbalance between the pressure of the liquid columns and the osmotic “pressure”, which will be compensated by the flow of a fresh portion of solvent 60 into capillary 2 through a semipermeable membrane 6. Thus, the length the diffusion path will be maintained in the capillary approximately constant, and a minor error 65 was surviving with the help of a `` UT-10 '' ultra-thermostat. Nitrogen was continuously fed into channel 1 — 10 cm ^e / min; the diffusion path length was set approximately. 1 cm

The tests were carried out on a chromatograph under the following analysis conditions: flame-ionization detector, column Zx 0.5 mm, length 1 m, filled with 10 weight. % squalane on chromosorb W, column thermostat temperature 80 ° C, sample dosing was carried out by a gas dosing tap, dose volume was 0.125 cm ^, dosing reproducibility was not worse than 1%, the concentration of hexane in nitrogen at the output of the device was 0.01 vol. % After a continuous seven-day purge, the following results were obtained. The level of the phase boundary remained almost constant, and the change in the concentration of hexane in nitrogen did not exceed 5%.

The implementation of the invention will significantly improve the quality of determining the metrological characteristics of analytical instruments by increasing the accuracy of calibration and reducing the complexity of processing the results.

Claims (1)

Schenn in the vessel 7 with the solvent 8. Channels 1 and 4 are connected by pipeline 9. The device operates as follows. When the capillary 2 is immersed in a pump 7 with a solvent 8 due to the unilateral permeability of the solvent. The cut of the semipermeable membrane 6 produces an osmotic pressure, described for low salt concentrations, is quite good with the van't Hoff P CRT equation, where C is the salt concentration; R is a universal gas constant; T is the temperature. Under the action of this pressure, the diluent 8 penetrates the capillaries p 2 until the pressure of the columns of liquids in the capillaries counterbalances the osmotic pressure, and P, and the pressure of the columns x of the liquids P to the bottom of the caps p 2, is determined by the ratio | Pi-d Vi -daiii, where f - specific gravity is analyzed. th substance; hj is the height of the substance being analyzed; 2. - the proportion of salt solution; h а .- height of the salt growth column of the thief, In steady-state equilibrium, there will be a definite length of the diffusion path from the surface of the liquid being analyzed to the carrier gas stream and the analyte concentration in the stream. You can determine it using the formula g-y O TTCH .. i LQ where. C - concentration analyzing the 1st substance in the meniscus of the liquid; D is the vapor diffusion coefficient in the carrier gas; S is the cross-sectional area of the capillary; L is the diffusion path length; Q - flow - carrier. As a result of evaporation, analyze. After a certain amount of time, the diffusion path length will increase, which will lead to a decrease in the concentration of the analyte in the carrier gas stream. At the same time, the total height of the liquid columns will decrease, which will disturb the equilibrium between the pressure of the liquid columns and the osmotic pressure, which will be compensated by the flow of a fresh portion of the solvent into the capillary volume 2 through the semi-permeable membrane 6. In this way, the diffusion path length will be maintained the capillary is approximately constant, and a minor error will be determined by the difference in the weights of the analyte and saline. For experimental verification of the proposed device, a mock-up was made. The capillary tube is made of a glass tube with an inner diameter of 2 mm. As a salt solution was used a solution of magnesium sulfate in water. The analyte is hexane. The temperature of 25 ° C was maintained using the UT-10 Ultratermostat. Channel 1 was continuously supplied with nitrogen — 10, the length of the diffusion path was set approximately. 1 cm. The tests were carried out on a chromatograph under the following conditions of analysis: a flame ionization detector, column Sx 0.5 mm, 1 m long, filled with 10 weight. % squalane on chromosorb W, column thermostat temperature, sample dosing was performed with a gas metering tap, dose volume was 0.125 cm, reproducibility of dosing was no worse than 1%, the concentration of gaxane in nitrogen at the device output was 0.01 vol. % After a continuous seven day purge, the following results were obtained. The level of the phase boundary remained almost constant, and the change in the concentration of hexane in nitrogen did not exceed 5%. Implementation of the invention will significantly improve the quality of determining the metrological characteristics of analytical instruments by increasing the calibration accuracy and reducing the complexity of processing the results. Formula of the Invention A device for preparing calibration gas-vapor mixtures containing a carrier gas supply channel, a capillary particle partially filled with the substance being analyzed and connected with an upper end to a channel for the delivery of a gas carrier, characterized in that in order to ensure the stability of the concentration gas mixture by maintaining a constant level of the analyte in the capillary, it is equipped with a semipermeable membrane fixed on the lower end of the capillary, and a container with a solvent in which the lower end of the capillary is placed, and above the membrane in the capillary there is a salt solution. Sources of information taken into account in the examination 1. Gas chromatography. Proceedings of NIITEKHIM, M ,, 1964, vol. 1, s. 72-75, .2, Nerezky V.G., et al., Gas chromatographic methods for analyzing impurities M., Nauka, 1970, p. 202-204. Goal