RU2237893C2 - Method of determining o- and m-nitrotoluenes in air - Google Patents

Abstract

FIELD: analytical methods.

SUBSTANCE: determination of o- and m-nitrotoluenes in air comprising sampling, modifying piezosensor with active sorbent, passing sample along with carrying gas through detection cell, and recording piezosensor signal is characterized by that active sorbent utilized is triton X-100 taken in amount 10-12 mcm, carrying gas is air, which is passed through detection cell before passage of sample, and passage velocity and passage time in both cases are 45-55 cm3/min and 2-3 min. Advantages of the method are: essentially simplified analytical equipment, diminished analysis and modification times, reduced number reagents utilized, lowered determination temperature from 210оС to 20-25оС.

EFFECT: accelerated analytical procedure and reduced expenses.

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Description

The invention relates to the analytical chemistry of organic compounds and can be used to detect o- and m-nitrotoluenes in the air of the working zone of the enterprises of the perfumery, soap and aniline-paint industries.

Known gas chromatographic method for the determination of o - and m-nitrotoluene in the air [EG Ivanyuk, Yu.A. Kolievskaya. Gas chromatographic determination of nitrotoluene and toluidine in the air of industrial premises // Plant, lab. - 1977. - T. 43, No. 2. - S. 157-158].

The determination of o- and m-nitrotoluene is carried out on a column 1 m long, filled with dinochrome P with a mixture of liquid phases, 1% each, apieson Z, benton 34 and PFMS-4. The flow rate of the carrier gas (nitrogen) 30 ml / min, hydrogen - 60 ml / min, air - 600 ml / min. Column temperature 164 ° С, evaporator 250 ° С. analysis duration> 10 min. For analysis, 20 l of air was taken, passed at a speed of 1 l / min through a sampling tube filled with KSK silica gel with a grain diameter of 0.5 mm. The sample was washed with 2.5 ml of ethyl alcohol.

The closest in technical essence and the achieved effect is a method for determining o- and m-nitrotoluene in air using a piezosensor (AT-cut, nominal vibration frequency of 9 MHz), a modified phthalocyanine film of copper (II) obtained by vacuum deposition on electrodes.

The determination of o- and m-nitrotoluenes is based on a preliminary translation of the analytes into NO ₂ . The released NO ₂ then passes through the gas pipeline to the detection cell in which the piezosensor is located. The temperature of the detection cell is 210 ° C. The carrier gas is nitrogen.

[Т.A.Rocha-Santos, M.T.Gomes, А.С.Duarte, J.P.Oliveira A quartz crystal microbalance sensor for determination of nitroaromatics in landfill gas // Talanta. - 2000. - V. 51. - P. 1149-1153.].To eliminate the influence of humidity, a pre-column filled with a molecular sieve is located in front of the detection cell.

[T.A. Rocha-Santos, MTGomes, A.C. Duarte, JP Oliveira A quartz crystal microbalance sensor for determination of nitroaromatics in landfill gas // Talanta. - 2000. - V. 51. - P. 1149-1153.].

The disadvantage of the prototype is the complexity, significant duration and high temperature analysis, the duration of the modification of the piezosensor.

An object of the invention is to simplify the hardware design, reducing the temperature and duration of the analysis.

The problem is achieved in that in the method for determining o- and m-nitrotoluenes in air, including sample preparation, modifying the piezosensor with an active sorbent, passing a sample and a carrier gas through the detection cell, recording the piezosensor signal, it is new that an active sorbent is used X-100 triton with a mass of 10-12 μg, air is used as a carrier gas, which is passed through a detection cell before passing samples through it, and the flow rate and transmission time in both cases are accordingly, 45-55 cm ³ / min and 2-3 min.

The technical result consists in a significant simplification of the hardware design, increasing the expressness of the analysis and reducing the number of reagents used.

The maximum permissible concentration of o- and m-nitrotoluenes in the air of the working zone is 0.001 g / m ³ .

The method is carried out according to the following procedure

Sensor Modification As a piezosensor modifier, Triton X-100 previously dissolved in acetone (polyethylene glycol ether, is n- (1,1,3,3-tetramethyl) phenyl ether of polyethylene glycol) was used [Petsev N., Kotsev N. Handbook of gas chromatography. - M.: Mir, 1987. - 260 p.].

On both electrodes (diameter 5 mm, area 0.28 cm ² ), a piezosensor (AT slice, quartz density 2600 kg / m ³ ) with an eigenfrequency of 8 MHz was applied with a syringe using Triton X-100, dissolved in acetone in an amount of 10-12 μg ( concentration of 1 mg / cm ³ ). Then placed in an oven at 60 ° C (evaporation of the solvent).

The course of determination. A previously modified piezosensor based on volume acoustic waves was placed in the reaction vessel of the detection cell. Before starting work, water was supplied into the “shirt” through the nozzles from the thermostat to bring the cell temperature to a predetermined level. The piezosensor 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 carrier gas (air) was first pumped with a microcompressor at a flow rate of 45-55 cm ³ / min for 2-3 minutes and then the analyzed air sample containing o- and m-nitrotoluene, also at a flow rate of 45-55 cm ³ / min for 2-3 minutes.

Changes in the resonant frequency of the sensor (the difference in the frequencies of the oscillations of the piezosensor in air and in the analyzed gas sample) was calculated by the Sauerbrey G.G. formula Verwendung von schwingquarzenzen zur wagung dunner schlichten und zur microwagung // Z. Phys. - 1959. - Bd. 155. - S. 206-221].

To remove the sample from the reaction vessel and regenerate the piezosensor, the tube 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.

The method is illustrated by the following examples.

Example 1

Sensor Modification As a piezosensor modifier, triton X-100, previously dissolved in acetone, was used.

On both electrodes (diameter 5 mm, area 0.28 cm ² ) of the piezosensor (AT slice, quartz density 2600 kg / m ³ ) with a natural frequency of 8 MHz, a Triton X-100, dissolved in acetone in an amount of 8 μg (concentration 1 mg / cm ³ ). Then placed in an oven at 60 ° C (evaporation of the solvent).

The course of determination. The piezosensor was placed in the detection cell, where air was supplied (flow rate of 50 cm ³ / min) for 2 minutes, then an analyzed sample containing o- and m-nitrotoluenes was pumped with a microcompressor at the same flow rate. The content of o- and m-nitrotoluenes is directly proportional to the difference in the frequencies of the oscillations of the piezosensor in air and in the analyzed sample.

The method is not feasible, since the recorded signal (ΔF, Hz) is unstable. The results are shown in table 1.

Example 2. Modification of the sensor was carried out analogously to example 1, but the mass of the active sorbent (Triton X-100, dissolved in acetone) 10 μg, the flow rate of the carrier gas and the analyzed gas sample 25 cm ³ / min. Analyzed as described in example 1. The method is feasible. The duration of the analysis is 5-8 minutes. The results are shown in table 1.

Example 3. The modification of the sensor was carried out analogously to example 1, but the mass of the active sorbent (Triton X-100 dissolved in acetone) was 12 μg, the flow rate of the carrier gas and the analyzed gas sample was 50 cm ³ / min. Analyzed as described in example 1. The method is feasible. The duration of the analysis is 5-8 minutes. The results are shown in table 1.

Example 4. The modification of the sensor was carried out analogously to example 1, but the mass of the active sorbent (Triton X-100 dissolved in acetone) was 12 μg, the flow rate of the carrier gas and the analyzed gas sample was 75 cm ³ / min. Analyzed as described in example 1. The method is feasible. The duration of the analysis is 5-8 minutes. The results are shown in table 1.

Example 5. The modification of the sensor was carried out analogously to example 1, but the mass of the active sorbent (Triton X-100 dissolved in acetone) was 14 μg, the flow rate of the carrier gas and the analyzed gas sample was 75 cm ³ / min. Analyzed as described in example 1. The method is not feasible, since the surface of the sorbent film is destroyed. The results are shown in table 1.

Example 6. The modification of the sensor was carried out analogously to example 1, but the mass of the active sorbent (Triton X-100 dissolved in acetone) was 16 μg, the flow rate of the carrier gas and the analyzed sample was 50 cm ³ / min. Analyzed as described in example 1. The method is not feasible. The results are shown in table 1.

Example 7. The modification of the sensor was carried out analogously to example 1, but the mass of the active sorbent (Triton X-100 dissolved in acetone) was 16 μg, the flow rate of the carrier gas and the analyzed sample was 25 cm ³ / min. Analyzed as described in example 1. The method is not feasible, since the recorded signal (ΔF, Hz) is unstable. The results are shown in table 1.

In the table. 2 shows a comparative description of the prototype and the proposed method for various parameters.

From examples 1-7 and tables 1 and 2, it follows that the positive effect of the proposed method is achieved with a sorbent mass (Triton X-100) of 10-12 μg (concentration of TX-100 solution in acetone 1 mg / cm ³ ), gas flow rate the carrier and the analyzed air sample 45-55 cm ³ / min. These conditions make it possible to determine o- and m-nitrotoluenes in air. When reducing the mass of the sorbent (example 1), the flow rate of the carrier gas and the analyzed gas sample (example 2), the sensitivity of the modified piezosensor decreases with respect to o- and m-nitrotoluenes. The increase in the mass of the sorbent (Triton X-100 dissolved in acetone) (example 7), the flow rate of the carrier gas and the analyzed sample (example 5) leads to the destruction of the surface of the sorbent film and signal instability.

A positive effect on the proposed method is achieved due to the fact that the active sorbent used (X-100 triton dissolved in acetone) allows the detection of trace amounts of o- and m-nitrotoluenes in the analyzed sample (Table 1), using Triton X-100 as a solvent acetone allows you to get reproducible signals. The choice of the optimal sorbent mass (10-14 μg) and air flow rate increases the sensitivity of the modified piezosensor. Lowering the analysis temperature from 164 to 20-25 ° C allows for the rapid determination of o- and m-nitrotoluenes in places of their local emissions.

Compared with the prototype, the proposed technical solution has the following advantages:

- significantly simplifies the hardware design analysis;

- the duration of the analysis is reduced from 10 minutes to 5-8 minutes;

- the number of reagents used in the analysis is reduced;

- the temperature of determination decreases from 210 to 20-25 ° C.

Claims (1)

A method for determining o- and m-nitrotoluene in air, including sample preparation, modifying the piezosensor with an active sorbent, passing a sample and a carrier gas through a detection cell, recording a piezosensor signal, characterized in that X-100 triton with a mass of 10 is used as an active sorbent -12 μg, air is used as a carrier gas, which is passed through the detection cell before passing samples through it, and the flow rate and transmission time in both cases are 45-55 cm ³ / min and 2-3 min, respectively.