RU2321846C1 - Method for determining micro-concentrations of ethyl spirits in steam-gas mixtures - Google Patents

Abstract

FIELD: analytical chemistry, possible use for determining concentrations of ethyl spirits in steam-gas mixtures using an array of piezo-electric quartz resonators with films.

SUBSTANCE: method for determining micro-concentrations of ethyl spirits in steam-gas mixtures includes extracting 3-5 cm³ of analyzed steam-gas mixture, injecting the sample into closed detection cell, on the lid of which 3 piezo-electric quartz resonators are mounted with base frequency of 40 Mhz, onto electrodes of which on two sides solutions are applied, respectively, polyethylene glycol of sebacate, polyethylene glycol of succinate and Triton X-100 in such a way, that after removing free solvents the mass of films amounts to 7-10 micrograms, responses of piezo-electric quartz resonators with films are simultaneously recorded over 1-2 minutes and formed into kinetic "visual imprint", on basis of area of which using a calibrating graph the concentration of ethyl spirits is determined.

EFFECT: correctness, precision, selectivity, speed and convenience of analysis.

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Description

The invention relates to analytical chemistry and can be used to determine the micro-concentrations of ethyl alcohol in gas-vapor mixtures using a static "electronic nose" (an array of mass-sensitive piezoelectric quartz resonators with films).

An object of the invention is to develop a method for determining the microconcentrations of ethyl alcohol in gas-vapor mixtures using an array of mass-sensitive piezoelectric quartz resonators with films and a special data processing algorithm that provides speed, accuracy, accuracy, selectivity and ease of determination.

The technical problem is achieved in that the method for determining the micro-concentrations of ethyl alcohol in gas-vapor mixtures consists in sampling 3-5 cm ^{3 of the} analyzed gas-vapor mixture, introducing the sample into a closed detection cell, on the lid of which 3 piezoelectric quartz resonators with a base frequency of 40 MHz are fixed, to the electrodes of each of which solutions of polyethylene glycol of sebacinate, polyethylene glycol of succinate and Triton X-100, respectively, are applied on both sides

(polyoxyethylene monooctylphenyl ether) so that after removal of free solvents the mass of the films is 7-10 μg; The responses of piezoelectric quartz resonators with films are simultaneously recorded for 1-2 minutes and are formed into a kinetic “visual imprint”, the area of which using the calibration curve determines the concentration of ethyl alcohol.

The technical result consists in the development of a method for the rapid determination of micro-concentrations of ethyl alcohol in gas-vapor mixtures using a static "electronic nose" (a closed detection cell, on the lid of which piezoelectric quartz resonators with films are fixed), which allows the use of three different films to selectively detect the presence of ethyl alcohol vapors and determine its concentration in gas-vapor mixtures; reduce economic costs due to the repeated use of piezoelectric quartz resonators with films; to increase the mobility of the detecting device and to carry out measurements in real time in situ without prolonged sampling and the use of special samplers.

Figure 1 - "Visual prints" of the equilibrium gas phases of standard solutions:

standard 1 - distilled water;

standard 2 - a solution of ethyl alcohol in water with a concentration in the equilibrium gas phase of 0.002 mg / m ³ (selected as an example).

Figure 2 is a calibration graph in the coordinates S = f (with _et.s. , mg / m ³ ).

Figure 3 - "Visual imprint" of the analyzed samples of the vapor-gas mixture containing an unknown concentration of ethyl alcohol.

The method for determining the microconcentrations of ethyl alcohol in gas-vapor mixtures is implemented as follows. Three mass-sensitive piezoelectric quartz resonators with a base oscillation frequency of 40 MHz are fixed on the cover of a static "electronic nose", on each of which electrodes, on each side of the electrodes, certain volumes of solutions, respectively, of polyethylene glycol sebacinate, polyethylene glycol succinate and Triton X-100 followed by static by evaporation of free solvents in an oven. After removal of solvents, the film mass is 7-10 μg.

Three mass-sensitive piezoelectric quartz resonators with films - the minimum number of measuring elements in the matrix to implement the method and obtain reliable results.

Construction of a calibration graph. A series of standard aqueous solutions of ethyl alcohol is prepared with a vapor concentration in the equilibrium gas phase of 0-0.01 mg / m ³ . Select 3 cm ³ water-alcohol mixture and place in a bottle with a volume of 10 cm ³ .

After saturation of the gas phase with ethyl alcohol vapor through a polyurethane membrane, 3-5 cm ^{3 of the} equilibrium gas phase is taken with a syringe. The sample is quickly injected into the detection cell. At the same time, the oscillation frequency of three piezoelectric quartz resonators with films is recorded for 1-2 minutes and a petal diagram is constructed from this signal — a kinetic “visual imprint” of the equilibrium gas phase of aqueous solutions of ethyl alcohol (Fig. 1). Calculate the area of the "visual imprint" and build a calibration graph in coordinates S = f (with _et.sp. , mg / m ³ ) ( _figure 2).

Under identical conditions, samples of steam-gas mixtures with an unknown concentration of ethyl alcohol are analyzed, "visual imprints" of the signals of piezoelectric quartz resonators with films are constructed (Fig. 3). The area of the “visual imprint” (S, rel. Unit ² ) is calculated and the concentration of ethyl alcohol (with _eth.sp. , mg / m ³ ) is found from the calibration graph (FIG. 2).

The regeneration of the closed detection cell and films is carried out with dried laboratory air supplied to the detection cell with a compressor for 10 s. Silica gel is used as a desiccant.

The method is illustrated by the following example.

Example. Let us demonstrate the method by the example of the analysis of a gas-vapor mixture containing an unknown concentration of ethyl alcohol (exhaust air from a yeast-growing apparatus).

The electrodes of 3 piezoelectric quartz resonators with films with an eigenfrequency of 40 ± 5 MHz were modified on both sides by uniformly applying acetone solutions with a microsyringe, respectively, polyethylene glycol sebacinate, polyethylene glycol succinate and Triton X-100 so that after static evaporation of free solvents in an oven for 20 min at a temperature of not more than 40 ° C, the film mass was 7-10 μg.

Sample preparation of the analyzed samples was as follows. A series of standard aqueous solutions of ethyl alcohol was prepared with a vapor concentration in the equilibrium gas phase of 0-0.01 mg / m ³ . 3 cm ^{3 of a} water-alcohol mixture was taken and placed in a 10 cm volume bottle. After saturation of the gas phase with ethyl alcohol vapors for 10-15 minutes, 3-5 cm ^{3 of the} equilibrium gas phase was taken through a polyurethane membrane using a syringe.

A sample was injected into the detection cell. At the same time, the vibration frequency of all piezoelectric quartz resonators with films was recorded for 1-2 minutes, the total signal of which was formed in the form of kinetic "visual imprints" of the equilibrium gas phase of aqueous solutions of ethyl alcohol. The area of the “visual imprint” was calculated and a calibration graph was constructed in the coordinates S = f (c _et.sp. , mg / m ³ ).

Under identical conditions, a sample of a gas-vapor mixture with an unknown concentration of ethyl alcohol was _analyzed (with _et.sp. , mg / m ³ ), a “visual imprint” of the signals of piezoelectric quartz resonators with films was constructed (Fig. 3). The area (S, rel. Unit ² ) was calculated and the concentration of ethyl alcohol (C _et.s. , mg / m ³ ) was found according to the calibration schedule (Fig. ² ).

The concentration of ethyl alcohol in the analyzed sample was 0.0053 mg / m ³ .

To regenerate a closed detection cell and sorbent films, the system was purged with dried laboratory air for 10 s. Silica gel was used as a desiccant.

The duration of the analysis, taking into account sample preparation, is 10-15 minutes, the measurement time is 2 minutes, the number of measurements without updating the sensor array is 100. Repeated film deposition on the electrodes of piezoelectric quartz resonators is not more than 45 minutes.

The method is feasible. It is possible to determine the microconcentrations of ethyl alcohol in a gas-vapor mixture.

A change in the mass of films on the electrodes of piezoelectric quartz resonators, the nature of the adsorbent solutions deposited on the electrodes, algorithms for processing analytical information, a decrease in the number of sensors leads to an increase in the analysis error, a small difference in the “visual prints” of the standards and the analyzed samples, worsens the metrological characteristics of the method. An increase in the number of measuring elements in the matrix of more than three leads to a glut of information on the “visual imprint” and a decrease in the accuracy of the determination.

As follows from the example, figure 1, 2 and 3, the proposed method allows you to: quickly determine the micro-concentration of ethyl alcohol in a gas-vapor mixture; ensure high sensitivity of determination, increase the efficiency and mobility of the analysis, as well as reduce the time spent on sampling and sample preparation.

Claims (1)

The method for determining the microconcentrations of ethyl alcohol in gas-vapor mixtures, which consists in taking 3-5 cm ^{3 of the} analyzed gas-vapor mixture, introducing the sample into a closed detection cell, on the lid of which 3 piezoelectric quartz resonators with a base frequency of 40 MHz are fixed, on the electrodes of each of which on both sides solutions, respectively, of polyethylene glycol of sebacinate, polyethylene glycol of succinate and Triton X-100 are applied so that after removal of free solvents the mass of the films is 7-10 μg, the responses are piezoelectric quartz resonators with films are simultaneously fixed for 1-2 min and formed into a kinetic “visual imprint”, the area of which using the calibration curve is used to find the concentration of ethyl alcohol.

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