RU2284031C1 - Method for determining fumes of acetaldehyde in the air of workzone - Google Patents

Abstract

FIELD: analytical chemistry.

SUBSTANCE: selected sample is injected into detecting cell with piezo-quartz resonator, electrodes of which are previously modified by a solution Tween-40 (polyoxiethylenesorbitolmonopalmitate) in chloroform so that mass of film after removal of solvent is 15-20 micrograms. For aforementioned purpose film of modifier is dried at 40°C for 30 minutes. Registration of analytical signal is performed in form of response of modified electrodes of piezo-quartz resonator after injection of probe into detection cell, calculation of acetaldehyde concentration is performed using formula ΔF=4,1·c, where ΔF - response of modified piezo-quartz resonator, Hz; c - concentration of acetaldehyde, mg/m³.

EFFECT: decreased time spent on determining acetaldehyde and decreased error of determining process.

2 tbl, 6 ex

Description

The invention relates to the analytical chemistry of organic compounds and can be used to determine acetaldehyde vapor in the air of the working zone of chemical and other industrial enterprises.

The closest in technical essence and the achieved effect is a method for determining acetaldehyde vapor in the air of a working zone using a gas-liquid chromatograph with a flame ionization detector [Methodological instructions for gas chromatographic measurement of concentrations of ethylene, propylene and acetaldehyde in the air of a working zone: guidelines for determining harmful substances in air / ed. Kuzminykh A.N., Makhidonskoy R.N., Ovechkina V.R. - M .: printing house of the Ministry of Health of the USSR, 1983. - Sat. No. 19. - S.171-174,], including sampling, preparing the detection device (gas chromatographic column) for analysis and detection. Sampling is carried out without concentration. Samples are taken in gas pipettes, which are pre-purged with a 5-fold volume of the analyzed air. The vessels are closed with plugs. The column is filled with polysorb under vacuum and conditioned at 150 ° C for 8-10 hours in a stream of nitrogen. The determination of acetaldehyde is carried out in isothermal mode, 3 ml of the sample is introduced into the evaporator through a self-sealing membrane. Acetaldehyde is determined by absolute calibration by measuring the area of the chromatographic peak. Calibration vapor-air mixtures are prepared in separate pipettes by introducing a certain amount of pre-chilled acetaldehyde. Chromatography of calibration mixtures is carried out under the same conditions as the samples. The range of measured concentrations of acetaldehyde is 3-30 mg / m ³ (the maximum permissible concentration of acetaldehyde in the air of the working area is 5 mg / m ³ ). Measurement error ± 25%.

The disadvantages of the method are the duration of the preparation of the detecting device (gas chromatographic column), the complexity and high cost of hardware design, a relatively high error of determination.

An object of the invention is to develop a method for the determination of acetaldehyde vapor in the air of the working area, the intensification of the process for determining acetaldehyde, reducing the error of determination.

The stated technical problem is achieved by the fact that in the method for determining acetaldehyde vapor in the air of the working area, including sampling, preparing the detection device for operation, detection with registration of the analytical signal and calculation of the concentration of acetaldehyde according to the calibration graph, it is new that the selected sample is introduced into the cell detection with a piezoelectric crystal, the electrodes of which are previously modified with a solution of Tween-40 (polyoxyethylene sorbitol monopalmitate) in chloroform so that ace film after solvent removal was 15-20 g, which film modifier was dried at 40 ° C for 30 min, the analytical signal recording is carried out in a modified response piezoelectric resonator electrodes after the introduction of the sample into the detection cell, the calculation of the concentration of acetaldehyde produced by the equation

ΔF = 4.1 · s,

where ΔF is the response of the modified piezoelectric crystal resonator, Hz;

C is the concentration of acetaldehyde, mg / m ³ .

The technical result of the proposed method is achieved by modifying the electrodes of the piezoelectric crystal resonator with a Tween-40 film deposited from a solution in chloroform and exhibiting sorption affinity for acetaldehyde. The application of a film with a sorbent mass of 15–20 μg on the strain-sensitive region of the piezoresonator helps to increase sensitivity and reduce the error of determination.

The method is carried out according to the following method.

1) Sampling. 2 cm ³ acetaldehyde is placed in a glass casing with a semi-permeable lid, the equilibrium gas phase of acetaldehyde is taken with a syringe with a capacity of 10 cm ³ , diluted with air to the required concentration, kept at room temperature for 5 minutes, then, through a sealed shutter, they are introduced into the detection cell containing a piezoelectric crystal with Tween-40 film.

2) Preparation of the detecting device. A solution of Tween-40 sorbent in chloroform is applied to the aluminum electrodes of the AT-cut piezoelectric quartz resonator with a natural vibration frequency of 8-10 MHz using a microsyringe so that after removing the solvent in the oven for 30 minutes at 40 ° C, the modifier film mass is 15-20 μg .

3) Determination of acetaldehyde vapor. The modified piezoelectric crystal resonator is placed in the detection cell with the injection injection of the sample; before measuring 5 min, it is adapted to the medium of the cell. The piezoresonator is stabilized if the frequency shift for 5 minutes is in the range of 10-15 Hz. Then, 5 cm ^{3 of} air containing acetaldehyde vapor is injected into the cell with a syringe at a concentration of 3 -20 mg / m ³ . Reading signals is carried out every 5 s until equilibrium is established in the sorption system. Based on the difference F _pl -F _c (F _pl is the vibration frequency of the piezoresonator modified with Tween-40 film, F _c is the vibration frequency of the piezoresonator during sorption of acetaldehyde vapor), the sensor response ΔF, Hz (maximum change in the frequency of sensor vibrations during sorption) is calculated. A calibration graph is constructed of ΔF versus acetaldehyde vapor concentration in air (s, mg / m ³ ). According to the equation of the graph, the acetaldehyde content in the analyzed air sample is found:

ΔF = 4.1 · s.

After the measurement, the detection cell and the film coating are regenerated by purging the system with air.

The duration of the analysis with sampling according to the full scheme, including the modification of the electrodes of the piezoelectric crystal and the subsequent regeneration of the detection cell, is 40 min.

The number of analyzes without replacing the coatings of a piezoelectric crystal is 150.

The time required to restore the sorbent, 10 minutes

The error in the determination of acetaldehyde vapor in air is ± 12%.

The method is illustrated by the following examples.

Example 1

A solution of Tween-40 in chloroform is applied to the electrodes of the piezoelectric quartz resonator with a syringe so that the film mass after evaporation of the solvent in an oven at 40 ° C for 30 min is 15 μg. Then the piezoresonator is placed in a static detection cell with injection injection of the sample, held for 5 minutes to establish a zero signal, inject the sample to be analyzed with a volume of 5 cm ³ using a syringe, and record the signal of the piezoresonator 10 seconds after injection of the sample. Using the difference F _PL -F _{s, the} sensor response ΔF is calculated and the equation of the calibration graph ΔF = 4.1 · s is used to find the acetaldehyde content in the analyzed air sample. The method is feasible. The results of the analysis are given in table 1.

The duration of the analysis with sampling according to the full scheme with the modification of the electrodes and the subsequent regeneration of the detection cell is 40 min.

The number of analyzes without replacing the coatings of a piezoelectric crystal is 150.

The time required to restore the sorbent, 10 minutes The error in the determination of acetaldehyde vapor in air is ± 12%.

Example 2

A solution of Tween-40 in chloroform is applied to the piezoelectric resonator electrodes with a syringe so that the mass of the film after removing the solvent in an oven at 40 ° C for 30 minutes is 20 μg. Next, analyze as described in example 1. The method is feasible. The results are shown in table 1.

Example 3

A solution of Tween-40 in chloroform is applied to the electrodes of the piezoresonator with a syringe so that the mass of the film after removing the solvent in an oven at 50 ° C for 30 minutes is 20 μg. Then they analyze it as indicated in Example 1. The method is not feasible, since the modifier decomposes, the “life” of the piezoresonator decreases without replacing the coating, and a significant drift of the zero signal is observed. The results are shown in table 1.

Example 4

A solution of Tween-40 in chloroform is applied to the electrodes of the piezoresonator with a syringe so that the mass of the film after removing the solvent in an oven at 30 ° C for 30 minutes is 20 μg. Next, analyze as described in example 1. The method is not feasible, since the temperature of 30 ° C does not provide complete removal of the solvent, which leads to a significant drift of the zero signal, an increase in the error of determination.

Example 5

Another modifier is applied to the piezoresonator electrodes with a microsyringe — a solution of polystyrene in toluene so that the film mass after removing the solvent in an oven at 40 ° C for 20 minutes is 15 μg. Next, analyze as indicated in example 1. The method is not feasible, since the analytical signal of the piezoresonator is at the noise level, there is a significant drift of the zero signal. The results are shown in table 1.

Example 6

Another modifier is applied to the piezoresonator electrodes with a microsyringe — a solution of squalane in chloroform so that the film mass after removing the solvent in an oven at 40 ° C for 20 min is 15 μg. Next, analyze as indicated in example 1. The method is not feasible, since the analytical signal of the piezoresonator is at the noise level, there is a significant drift of the zero signal. The results are shown in table 1.

Some characteristics of the proposed method and prototype are compared in table.2.

From examples 1-6 and tables 1 and 2, it follows that the positive effect of the proposed method is achieved when the mass of the Tween-40 sorbent film is 15-20 μg after removing the solvent in an oven for 30 min at 40 ° C (examples 1 and 2). With a decrease or increase in the mass of the sorbent, the sensitivity of the modified piezoelectric crystal resonator with respect to acetaldehyde vapor in the air decreases, the error of determination increases. Removing the solvent in an oven at 50 ° C leads to decomposition of the modifier, a decrease in the “life” of the piezoresonator without replacing the coating, and a significant drift of the zero signal (Example 3). At 30 ° C in the drying cabinet does not completely remove the solvent, which leads to a significant drift of the zero signal and an increase in the error of determination (example 4). The use of other modifiers (examples 5 and 6) does not allow the determination of acetaldehyde vapor in the air of the working zone.

Thus, the proposed method for determining the vapor of acetaldehyde in the air of the working area in comparison with the prototype allows you to:

1) reduce the preparation time of the detecting device from 8-10 hours to 30 minutes;

2) to intensify the process of determining acetaldehyde, i.e. reduce analysis time from 90-120 to 40 min;

3) reduce the error of determination from 25 to 12%.

Table 1 Examples of the method Example Number Modifier Solvent The mass of the modifier m, mcg Solvent removal temperature, ° C Analytical signal, Hz Polling time, s Regeneration time, min Determination error,% The implementation of the method one Tween-40 chloroform fifteen 40 35 10 10 12.0 feasible 2 Tween-40 chloroform twenty 40 33 10 10 12.6 feasible 3 Tween-40 chloroform twenty fifty 28 10 10 13,4 not feasible four Tween-40 chloroform twenty thirty 26 10 10 14.8 not feasible 5 polystyrene toluene fifteen 40 8 fifteen 10 18.5 not feasible 6 squalane chloroform fifteen 40 9 5 10 14.5 not feasible

table 2 Comparison of the prototype and the proposed method Parameter Prototype The proposed method Duration of preparation of the detecting device 8-10 h 30 minutes The duration of the analysis, min 90-120 40 Determination error ± 25% ± 12% The minimum detectable concentration of acetaldehyde, mg / m ³ 3 3

Claims (1)

A method for determining acetaldehyde vapor in the air of a working area, including sampling, preparing a detecting device for operation, detecting with recording an analytical signal and calculating acetaldehyde concentration according to a calibration graph, characterized in that the selected sample is introduced into a detection cell with a piezoelectric crystal, the electrodes of which are previously modified a solution of Tween-40 (polyoxyethylene sorbitol monopalmitate) in chloroform so that the mass of the film after removal of the solvent was 15-20 m kg, for which the modifier film is dried at 40 ° C for 30 min, the analytical signal is recorded in the form of a response of the modified electrodes of the piezoelectric crystal after the sample is introduced into the detection cell, the acetaldehyde concentration is calculated by the equation ΔF = 4.1 · s, where ΔF is the response of the modified piezoelectric crystal resonator, Hz; C is the concentration of acetaldehyde, mg / m ³ .