Method for determining fumes of butyric acid in presence of palmitic acid and stearic acid in the air of work zone

FIELD: analytic chemistry of organic compounds, possible use for determining fumes of butyric acid in presence of palmitic and stearic acids in the air of work zone of chemical and other industrial plants.

SUBSTANCE: in the method for determining fumes of butyric acid in presence of palmitic and stearic acids in the air of work zone, including taking of a sample, preparation of detecting device for operation, injection of sample into detecting cell and registration of analytic signal, calculation of concentration of butyric acid in accordance to calibrating graph, taken sample is injected into detecting cell with piezo-quartz resonator, electrodes of which are preliminary modified by application of polyethyleneglykol-2000 sorbent onto them in acetone so, that mass of film after removal of solvent in drying stand during 30 minutes at 40°C amounts to 17-25 micrograms, registration of analytic signal is performed after injection of sample into detecting cell in form of response of modified electrodes of piezo-quartz resonator, calculated on basis of difference of its oscillation frequencies prior to injection of sample and after balancing of sorption system with injected sample, concentration of butyric acid is calculated on basis of calibrating graph depending on aforementioned response from its concentration on basis of formula ΔF=3,5·c, where ΔF - response of modified electrodes of piezo-quartz resonator, Hz; c - concentration of butyric acid, mg/m3.

EFFECT: simplification and acceleration of analysis when determining butyric acid in presence of palmitic and stearic acids.

6 ex, 2 tbl

 

The invention relates to analytical chemistry of organic compounds and can be used to determine the vapor butyric acid in the presence of palmitic and stearic acids in the air of working zone enterprises of the chemical and other industries.

The closest in technical essence and the achieved effect is a photometric method for determining vapor butyric acid in the air of working zone, which consists in obtaining the methyl ester of the acid with subsequent determination by reaction with hydroxylamine hydrochloride and perchlorate iron, λ=490 nm [guidelines on the determination of harmful substances in the air. Issue 1-5. M: the Ministry of health of the USSR CRIA "Morflot", 1981. 253 C.]. For sampling from the air of the working area used adsorption vessels with silica gel. Maximum permissible concentration of butyric acid in the air of working zone is 10 mg/m3.

The disadvantages of the method are the need of sample preparation, preparation of solutions of hydroxylamine hydrochloride and perchlorate iron for each single definition, complexity and duration determine the vapor butyric acid.

An object of the invention is to develop a method for determining vapor butyric acid in the presence of palmitic and stearic acids in the air of the working zone with the adiya's sample preparation the reduction in the duration analysis.

The goal of the project is achieved in that in the method of determining vapor butyric acid in the presence of palmitic and stearic acids in the air of working zone, including sampling, preparation of the detecting device to work, the input sample in the cell detection and registration of the analytical signal, calculation of the concentration of butyric acid on the calibration curve, the selected sample is introduced into the cell detection with piezoquartz resonator, the electrodes of which is pre-modified by applying them to the solution of the sorbent of polyethylene glycol-2000 (PEG-2000) in acetone so that the mass of the film after removal of the solvent in a drying Cabinet for 30 min at 40°was 17-25 mcg, the analytic signal is carried out after the entry into the cell detection samples in the form of the response of the modified electrode piezoquartz resonator calculated by difference frequency of its oscillations to the input of the sample and after the establishment of equilibrium sorption system with the introduced sample, the concentration of butyric acid calculated on the basis of the calibration curve according to the specified response from her concentration by the equation

ΔF=3,5·C

where ΔF - response of the modified electrode piezoquartz resonator Hz;

- the concentration of butyric acid, mg/m3.

The technical result of the proposed method is achieved by modification of electrodes piezoquartz resonator film PEG-2000, deposited from a solution in acetone and showing the sorption affinity for oil acid. The coating film with a mass of sorbent 17-25 µg testcustomer region of piezoresonator helps to increase the sensitivity and reduce errors in the determination.

The method is carried out by the following method.

1) Sampling. In a glass tube with a semi-permeable cover is placed 2 cm3butyric acid, a syringe with a capacity of 10 cm3select the equilibrium gas phase, diluted with air to the desired concentration, incubated at room temperature for 5 min, then through the sealed gate is introduced into the cell, detecting, containing piezoquartz resonator, a modified solution of PEG-2000 in acetone.

2) Preparation of the detecting device. On the aluminum electrodes piezoquartz resonator at-cut with the natural frequency of 8-10 MHz microspace put a solution sorbent PEG-2000 in acetone so that after removal of the solvent in a drying Cabinet for 30 min at 40°With the mass of the film modifier was 17-25 mcg.

3) Determination of vapor butyric acid. Modified petkar is the song data for the resonator is placed in the cell detection, before measurements 5 min adapt to the environment of the cell. Piezoresonator stable, if the shift of the oscillation frequency for 5 min is in the range of 10-15 Hz. Then in the cell with a syringe and injected 5 cm3air containing vapors of butyric acid at a concentration level of 5-20 mg/m3. The read signals are conducted every 5 seconds to establish equilibrium sorption system. On the difference between FPL-Fc(FPLthe oscillation frequency of piezoresonator modified film PEG-2000, Fcthe oscillation frequency of piezoresonator upon vapor sorption butyric acid) compute the response of the sensor ΔF, Hz (the maximum change in the oscillation frequency of the sensor during sorption). Construct a calibration graph of ΔF vapor concentration of butyric acid in the air (mg/m3). The equation of the graph find the content of butyric acid in the analyzed air samples:

ΔF=3,5·c.

After measuring regenerate cell detection and film coating scavenging systems laboratory air.

Duration analysis with sampling for the full scheme, including the modification of electrodes piezoquartz resonator and the subsequent regeneration of cell detection, 30 minutes

The number of analyses without replacement coatings piezoquartz resonator 200.

The time required for vosstanovleniya, 10 minutes

The error in the determination of vapor butyric acid in the air ±15%.

The definition of palmitic and stearic acids in the analyzed air using piezoquartz resonator, the electrodes of which is modified by a solution of PEG-2000 in acetone, were conducted by the method similar to those described above.

The method is illustrated by the following examples.

Example 1

In a glass tube with a semi-permeable lid was placed 2 cm3butyric acid, a syringe with a capacity of 10 cm3selected equilibrium gas phase was diluted with air to the desired concentration was kept at room temperature for 5 min, then through the sealed gate was injected into the cell detection, containing piezoquartz resonator, a modified solution of PEG-2000 in acetone.

To the electrodes of piezoquartz resonator microspace inflicted a solution of PEG-2000 in acetone so that the mass of the film after removal of the solvent in a drying Cabinet at 40°C for 30 min was 17 µg. Then piezoresonator was placed in a static cell detection with injection sample introduction, kept 5 min to establish a zero signal was injected with a syringe and analyzed a sample of 5 cm3and recorded the signal piezoresonator after 15 s after sample injection. On the difference between FPL-Fcexpected response of the sensor is Δ F, the equation of the calibration curve ΔF=3,5·with found the content of butyric acid in the analyzed sample of air. Way feasible. The results of the analysis are given in table 1.

Duration analysis with sampling by the full scheme with a modification of electrodes and the subsequent regeneration of the cell detection is 30 minutes

The number of analyses without replacement coatings piezoquartz resonator 200.

The time required to restore the sorbent, 10 minutes

The error in the determination of vapor butyric acid in the air 15%.

The definition of palmitic and stearic acids in the air with the use of piezoquartz resonator, the electrodes of which is modified by a solution of PEG-2000, was carried out similarly to the described method. Film PEG-2000, applied to the electrodes piezoquartz resonator from a solution in acetone, does not show the sorption affinity for palmitic and stearic acids, the analytical signal is at the noise level increases the measurement error. Therefore, palmitic and stearic acid does not interfere with the determination of vapor butyric acid in the air. The method is not feasible. The results are shown in table 1.

Example 2

Selection of vapor butyric acid was carried out similarly to example 1.

To the electrodes of piezoresonator microspace inflicted a solution of PEG-2000 in acetone so that the donkey removal of the solvent in a drying Cabinet for 30 min at 40° With the weight of the film modifier was 25 µg. It was further analyzed as described in example 1. Way feasible. The results are shown in table 1.

Example 3

Selection of vapor butyric acid was carried out similarly to example 1.

To the electrodes of piezoresonator microspace inflicted a solution of PEG-2000 in acetone so that after removal of the solvent in a drying Cabinet for 30 min at 50°With the mass of the film modifier was 25 µg. It was further analyzed as described in example 1. The method is not feasible, because the decomposition of the modifier decreases the life of piezoresonator without replacement coverage, there is a significant drift of the zero signal. The results are shown in table 1.

Example 4

Selection of vapor butyric acid was carried out similarly to example 1.

To the electrodes of piezoresonator microspace inflicted a solution of PEG-2000 in acetone so that after removal of the solvent in a drying Cabinet for 30 min at 30°With the mass of the film modifier was 25 µg. It was further analyzed as described in example 1. The method is not feasible, as the temperature of 30°not ensure a complete removal of the solvent, which leads to a significant drift of the zero signal, the increase of error definitions.

Example 5

Selection of vapor butyric acid was carried out similarly to example 1.

To the electrodes of Pietrasanta the ora-microspace inflicted another modifier - the solution of TBPA (tetrabenzoporphyrin) in acetone so that after removal of the solvent in a drying Cabinet for 30 min at 40°With the mass of the film modifier was 17 µg. It was further analyzed as described in example 1. The method is not feasible, as the analytical signal of piezoresonator is the noise level, there is a significant drift of the zero signal. The results are shown in table 1.

Example 6

Selection of vapor butyric acid was carried out similarly to example 1.

To the electrodes of piezoresonator microspace inflicted another modifier solution of squalane in chloroform so that after removal of the solvent in a drying Cabinet at 40°C for 30 min weight film modifier was 17 µg. It was further analyzed as described in example 1. The method is not feasible, as the analytical signal of piezoresonator is 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 mapped in table 2.

From examples 1-6 and table 1 and 2 it follows that the positive effect of the proposed method is achieved if the mass of the film sorbent PEG-2000, equal 17-25 mcg, after removal of the solvent in a drying Cabinet for 30 min at 40°With (examples 1 and 2). By reducing or increasing the mass of the sorbent decreases the setting of the modified piezoquartz resonator with respect to the pairs of butyric acid in the air, increases the measurement error. Removal of the solvent in a drying Cabinet at 50°leads to degradation of the modifier, the reduction of the "lifetime" of piezoresonator without replacement coverage, a significant drift of the zero signal (example 3). At 30°in a drying Cabinet does not fully remove the solvent, resulting in a significant drift of the zero signal and the increase of error definitions (example 4). The use of other modifiers (examples 5 and 6) does not allow to define a pair of butyric acid in the presence of palmitic and stearic acids in the air. Film PEG-2000, applied to the electrodes piezoquartz resonator from a solution in acetone, does not show the sorption affinity for palmitic and stearic acids, the analytical signal is at the noise level increases the measurement error. Therefore, palmitic and stearic acid does not interfere with the determination of vapor butyric acid in the air.

Thus, the proposed method of determining vapor butyric acid in the presence of stearic and palmitic acids in the air compared with the prototype allows you to:

1) to define a pair of butyric acid in the presence of palmitic and stearic acids in the air of working zone;

2) delete the stage of sample preparation;

2) to reduce analysis time from 120 min to 30 min/p>

Table 1

Examples of the method
Number exampleAcidModifierSolventWeight modifier, mcgTemperature solvent removal, °CAnalytical signal, HzThe time of the survey,Regeneration time, minMeasurement error, %The implementation of the method
1OilPEG-2000acetone174041151015,0feasible
PalmiticPEG-2000acetone17408101016,8impossible
StearicPEG-2000acetone17409101016,4impossible
2OilPEG-2000acetone254038151015,8feasible
3OilPEG-2000acetone255026151017,4impossible
4OilPEG-2000acetone253023151017,8impossible
5OilTBPAacetone1740651018,9impossible
6Oilsqualanechloroform174010101016,8impossible

Table 2

Comparison of the prototype and the proposed method
The placeholderThe proposed method
Stage of sample preparationRequiredNo
The analysis duration, min12030

The method of determining vapor butyric acid in the presence of palmitic the stearic acid in the air of working zone, including sampling, preparation of the detecting device to work, the input sample in the cell detection and registration of the analytical signal, calculation of the concentration of butyric acid on the calibration curve, wherein the selected sample is introduced into the cell detection with piezoquartz resonator, the electrodes of which is pre-modified by applying them to the solution of the sorbent peg-2000 in acetone so that the mass of the film after removal of the solvent in a drying Cabinet for 30 min at 40°was 17-25 mcg, the analytic signal is carried out after the entry into the cell detection samples in the form of the response of the modified electrode piezoquartz resonator, calculated by difference frequency of its oscillations to the input of the sample and after the establishment of equilibrium sorption system with the introduced sample, the concentration of butyric acid calculated on the basis of the calibration curve according to the specified response from her concentration by the equation

ΔF=3,5·c,

where ΔF - response of the modified electrode piezoquartz resonator Hz;

C - concentration of butyric acid, mg/m3.



 

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3 tbl, 4 ex

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