RU2216016C1 - Method detecting hexane in air - Google Patents

Abstract

FIELD: analytical chemistry of organic compounds, detection of hexane in air of working zone of enterprises of petrochemical, tire, shoe, textile, leather and furniture-making industry, production of vegetable oil. SUBSTANCE: method detecting hexane in air includes preparation of sample, detection of hexane with piezoquartz sensor based on volume acoustic waves modified by active sorbent, injection of equilibrium gas phase of analyzed sample into detection cell, registration of analytical signal of sensor. Squalene in mass range from 10 to 18 micrograms is utilized in the capacity of modifier of sensor. EFFECT: raised sensitivity of analysis. 2 tbl

Description

 The invention relates to the analytical chemistry of organic compounds and can be used to detect hexane in the air of the working zone of oil refining, tire, shoe, textile, leather and furniture industries, as well as in the production of vegetable oils.

 The closest in technical essence and the achieved effect is a method for determining hydrocarbons in air using a piezoelectric quartz sensor modified with polytrimethylsilyl styrene [Grechnikov A.A. Piezoresonance determination of ammonia, asymmetric dimethylhydrazine and hydrocarbons in the air. Abstract ... cand. Chem. sciences. - M., 2000. - 24 p.].

 The disadvantage of the prototype is the low sensitivity of the determination of hexane in the air.

 An object of the invention is to increase the sensitivity of the analysis.

 The problem is achieved in that in the method for determining hexane in air, including sample preparation, hexane detection with a piezoelectric crystal based on volume acoustic waves, modified by an active sorbent, introducing the equilibrium gas phase of the analyzed sample into the detection cell, recording the sensor’s analytical signal, is new that squalane in the mass range of 10-18 μg is used as a sensor modifier.

 The technical result is to increase the sensitivity of the analysis.

The maximum allowable concentration of hexane in the air of the working area is 300 mg / m ³ .

 The method is carried out according to the following method.

Sampling. The analyzed air was previously passed through a concentrator containing phosphoric acid, and through lead acetate to remove amines, tertiary alcohols, epoxides, carboxylic acids and organic sulfur compounds, the air thus purified was collected in a gas pipette or glass syringe with a capacity of 100-150 cm ³ . Air samples for analysis were taken from a gas pipette or a glass syringe into small medical all-glass or combined syringes with a glass piston by puncture of a rubber gasket of a glass plug and introduced into a detection cell containing a piezoelectric crystal on acoustic waves.

 Sensor Modification Squalane used in gas chromatography to determine hydrocarbons was used as a modifier of the electrodes of the piezoelectric crystal.

 The course of determination. The electrodes of a piezoelectric crystal based on volume acoustic waves with an eigenfrequency of 8-10 MHz were modified by uniformly applying squalane solutions of a certain volume using a chromatographic microsyringe so that after removal of the solvent the sorbent film mass was 10-18 μg, then the sensor was dried and stabilized for 5-10 minutes

 A pre-prepared piezoelectric crystal based on volume-acoustic waves was placed in the reaction vessel of a thermostatic detection cell. Before starting work, water was supplied through the nozzles from the thermostat to the jacket of the detection cell to bring the cell temperature to a predetermined level. Then the piezoelectric quartz sensor was kept in the flow of dried laboratory air for several minutes until a stable analytical signal was obtained, and the sensor readings were measured. The calibration graph represents the dependence of the oscillation frequency of the piezoelectric crystal on the volume of the air sample introduced into the detection cell. A sample of the analyzed air was taken with a syringe and introduced directly into the reaction vessel of the cell through an inlet pipe equipped with a silicone gasket. The stopwatch counted the time during which the signal of the piezoelectric crystal did not change. The difference between the signals of the piezosensor before and after the introduction of the sample served as a characteristic of quantitative determinations. To remove the sample from the reaction vessel and regenerate the piezoelectric crystal, the outlet pipe was opened and dried laboratory air was supplied until the sensor signal reached the initial level (before the sample was introduced). After that, the next measurement was performed in the cell.

Capture sensor response. The decrease in the operating frequency of the oscillations of piezoelectric quartz sensors on volume acoustic waves was calculated according to the Sauerbrey equation [Sauerbrey GG Messung von plattenschwingungen sehr kleiner amplitude durch lichtstrom-modulation // Z. Phys. - 1964. - Bd. 178. - S. 457 -471]:
Δf = -2.3 • 10 ^-6 • f $\genfrac{}{}{0ex}{}{\text{2}}{\text{O}}$ • Δm / A,
where Δf is the change in the frequency of the resonator; Δm is the mass of the modifier, g; f ₀ is the resonant frequency of the piezosensor, MHz, Hz; A is the surface area of the modifier, cm ² .

After introducing each sample into the detection cell, the resonance frequency of the piezoelectric crystal sensor was recorded and the relative frequency shift Δf _{a was} calculated by the equation:
Δf _a = f ₀ - f ₁ ,
where f ₀ and f ₁ are the oscillation frequencies of the sensor before and after analysis, Hz.

 The results of comparing the characteristics of the proposed method and prototype are presented in table. 2.

Examples of the method
Example 1

A film of squalane solution with a concentration of 1 mg / cm ^{3 and a} mass of 3 μg was formed on the electrodes of a piezoelectric quartz sensor based on volume-acoustic waves. The sensor was placed in the detection cell, kept in a stream of dried laboratory air until a stable analytical signal was obtained, then the readings were measured. A sample was taken with a syringe and introduced directly into the reaction vessel of the cell through an inlet pipe equipped with a silicone gasket. The stopwatch counted the time during which the signal of the piezoelectric crystal did not change. The difference between the signals of the piezosensor before and after the introduction of the sample is a characteristic of quantitative determinations. The method is feasible. The results of the determination of hexane by the proposed method are shown in table 1.

 The detection limit of hexane is 0.5 MPC, the noise level is ± 70 Hz.

 Example 2

 The preparation of the sensor was carried out by analogy with example 1. A squalane film weighing 5 μg was formed on the sensor electrodes. Then an air sample was analyzed. The method is not feasible. The results of the determination of hexane by the proposed method are shown in table 1.

 Example 3

 The preparation of the sensor was carried out by analogy with example 1. A squalane film weighing 8 μg was formed on the sensor electrodes. Then an air sample was analyzed. The method is feasible. The results of the determination of hexane by the proposed method are shown in table 1.

 The detection limit of hexane is 0.25 MPC, the noise level is ± 40 Hz.

 Example 4

 The preparation of the sensor was carried out by analogy with example 1. A squalane film weighing 12 μg was formed on the sensor electrodes. Then an air sample was analyzed. The method is feasible. The results of the determination of hexane by the proposed method are shown in table 1.

 The detection limit of hexane is 0.3 MPC, the noise level is ± 30 Hz.

 Example 5

 The preparation of the sensor was carried out by analogy with example 1. A squalane film weighing 15 μg was formed on the sensor electrodes. Then an air sample was analyzed. The method is feasible. The results of the determination of hexane by the proposed method are given in table. 1.

 The detection limit of hexane is 0.5 MPC, the noise level is ± 50 Hz.

 Example 6

 The preparation of the sensor was carried out by analogy with example 1. A squalane film weighing 18 μg was formed on the sensor electrodes. Then an air sample was analyzed. The method is feasible. The results of the determination of hexane by the proposed method are shown in table 1.

 Example 7

 The preparation of the sensor was carried out by analogy with example 1. A squalane film weighing 20 μg was formed on the sensor electrodes. Then an air sample was analyzed. The method is not feasible, since there is a breakdown in the generation of oscillations of the piezosensor.

 The detection limit of hexane is 0.75 MPC, the noise level is ± 80 Hz.

 From examples 1-7 and table 1 it follows that the greatest effect on the proposed method for determining hexane in air, including sampling and detection, is achieved using a sensor based on volume-acoustic waves, modified with a squalane film weighing 8 μg (example 3). With a decrease (example 1, 2) and an increase (examples 4-6) of the squalane film mass on the electrodes, the sensitivity of the piezosensors decreases and the detection limit of hexane increases or a breakdown in the generation of oscillations of the piezosensor is observed (example 7).

 Thus, the proposed method for the determination of hexane in the air in comparison with the prototype allows you to determine hexane in the air at concentrations at the level of 0, 25 MPC and higher.

Claims (1)

 A method for determining hexane in air, including sample preparation, hexane detection with a piezoelectric quartz sensor based on volume acoustic waves, modified with an active sorbent, input of the equilibrium gas phase of the analyzed sample into the detection cell, registration of the sensor’s analytical signal, characterized in that squalane is used as a sensor modifier in the mass range of 10-18 mcg.

Images