RU2312330C1 - Method of detecting automotive gasoline in air - Google Patents

Abstract

FIELD: analytical chemistry.

SUBSTANCE: method comprises preparing the detecting device for the operation, which includes modifying the electrodes of the piezoelectric quartz resonator at the 9-MHz frequency by the solution of β-cyclodextrin in ethanol so that the mass of the film after exposing piezoelectric sensor in drying cabinet at a temperature of 60°C to be 20 mg, blowing the air to be analyzed through the filtering member for 2 min, setting the prepared piezoelectric sensor into detector, connecting it in the circuit of the high-frequency quartz generator, recording the analytic signal as a frequency of oscillations of the quartz plate of the piezoelectric sensor when equilibrium in the sorption system is established, plotting a calibration curve, and determining the concentration of the gasoline vapors in air from the calibration curve.

EFFECT: enhanced sensitivity and reliability.

1 tbl, 1 ex

Description

The invention relates to the analytical chemistry of organic compounds and can be used to determine the vapor of gasoline in the air.

An object of the invention is to develop an express method for the determination of gasoline vapors in air at the level of maximum permissible concentrations (MPC) [GOST 2084-77. Gasoline automobiles] using a modified piezoelectric quartz resonator.

The stated technical problem is achieved in that the method for determining gasoline vapors in air is characterized by the fact that, for preparing the detecting device for operation, the electrodes of an AT-cut piezoelectric quartz resonator (SU 633136 A1, 11/15/1978; SU 267703 A1, 07/08/1970) with a frequency oscillations of 9 MHz are modified with a solution (β-cyclodextrin in ethanol so that the film mass after exposure of the piezosensor in an oven at 60 ° C is 2 μg, then the analyzed sample is blown through the filter cartridge for 2 minutes a gas mixture containing gasoline vapors, the prepared piezosensor is placed in the detector and included in the high-frequency generator circuit, the analytical signal is recorded in the form of the oscillation frequency of the piezosensor quartz plate when the thermodynamic equilibrium is established in the sorption system, as evidenced by the constant frequency of the piezosensor oscillations in time, a calibration graph is built by which the concentration of gasoline vapors is found.

The technical result of the proposed method is to develop an express method for the determination of gasoline vapors in air by modifying the electrodes of a piezoelectric quartz resonator with a solution (β-cyclodextrin in ethanol. The method is as follows.

1. Prepare a detection cell. The analyzed air is blown for 2 minutes through the filter cartridge into the detection cell, the cell is sealed with two plugs. The filter cartridge is a glass tube with three sections, two sections are filled with absorption powder to trap unsaturated and aromatic hydrocarbons that interfere with the determination, and one section is filled with granular calcium chloride to trap water vapor.

Absorption powder for trapping aromatic hydrocarbons. Fireclay is treated with a 3% solution of AgNO ₃ in sulfuric acid (p = 1.84 g / cm ³ ) at the rate of 0.2 cm ^{3 of} solution per 1 g of powder, mixed and placed in the first section of the filter cartridge.

Absorption powder for trapping unsaturated hydrocarbons. Dissolve 4 g of Hg ₂ SO ₄ in 20 cm ³ sulfuric acid qualification H.H. when heating and stirring, add 50 g of chamotte and mix it thoroughly until uniformly wetted. Then it is dried with constant stirring for 15-20 minutes, with the cooled chamotte powder the second section of the filter cartridge is filled. The third section is filled with granular calcium chloride.

The signs of working out the cartridge are the formation of calcium chloride that diffuse from moisture and the color of the powder treated with a solution of Hg ₂ SO ₄ . The use of a filter cartridge allows the determination of gasoline vapors in the air in the presence of water, unsaturated and aromatic hydrocarbons.

2. Modification of the sensor. A solution (β-cyclodextrin in ethanol is used as a surface modifier for the surface of the piezosensor electrodes. The sorbent is applied, for example, by the method of static evaporation of a drop, after removal of the solvent, the mass of the modifier should be 20 μg.

3. The method of determination. Before starting work, the analyzed air is blown through the filter cartridge for 2 minutes into the cell. The prepared piezosensor is placed in a cell and included in the circuit of a high-frequency crystal oscillator. The stopwatch counts the time after which the signal of the piezosensor does not change, and register the analytical signal. To carry out the next measurement, the sorption coating is regenerated and the detection cell is ventilated by passing dried laboratory air through it until the piezosensor signal reaches the initial level (before the sample is introduced). The vapor content of gasoline in the air is found on the calibration curve.

The duration of the analysis with sampling according to the full scheme, including the modification of the electrodes of the piezoelectric quartz resonator and the subsequent regeneration of the sorption coating, is 40 min.

The method for determining gasoline vapor in air is illustrated by the following example.

Example 1

A method for determining gasoline vapors in air involves preparing a detection cell, for which the analyzed air is blown through a filter cartridge into the detection cell, then a modified piezoelectric quartz resonator (β-cyclodextrin) is placed in it and included in the high-frequency quartz oscillator circuit, an analytical signal is recorded, and a calibration signal is built a graph according to which the concentration of gasoline vapors is found. rbtsionnogo coating and detecting ventilation passage therethrough laboratory air dried to yield pezosensorov cell signal to the initial level.

A solution of β-cyclodextrin in ethanol is applied to the electrodes of an AT-cut piezoelectric quartz resonator with a pre-measured oscillation frequency (f ₀ ) by static evaporation of a drop, after the piezosensor is exposed in an oven at 60 ° C, the frequency of the modified resonator is measured (f _pl ). The mass of the film is calculated according to the Sauerbrei equation [Sauerbrey GG Messung von plattenschwingungen sehr kleiner amplitude durch lichtstrom-modulation // Z. Phys. - 1964. - Bd. 178. -

Δf = -2.3 · 10 ^-6 · f ₀ ² · m / A,

where m is the mass of the modifier, g; f ₀ is the resonant frequency of the piezosensor, MHz; Δf = f _PL -fo - change in the frequency of the resonator, Hz; A is the surface area of the modifier, cm ² .

Before starting work for 2 minutes, air containing gasoline vapors is blown into the cell through a filter cartridge. After that, the prepared piezosensor is placed in the detector and included in the circuit of a high-frequency crystal oscillator. The signal of the piezosensor is recorded every second until the thermodynamic equilibrium is established in the system, as evidenced by the constancy of the oscillation frequency of the quartz plate of the piezosensor, and displayed on a personal computer monitor in the form of a kinetic sorption curve. For the next measurement, the sorption coating is regenerated and the detection cell is ventilated by passing dried laboratory air through it until the piezosensor signal reaches the initial level before the sample is introduced. The method is feasible.

The duration of the analysis with sampling according to the full scheme, including the modification of the electrodes of the piezoelectric quartz resonator and the subsequent regeneration of the sorption coating, is 40 min. The determination results are shown in the table.

In accordance with safety requirements, the maximum permissible concentration of gasoline vapors in the air is 100 mg / m ³ . The inventive method allows to determine the vapor of gasoline (GOST 2084-77. Gasoline for automobiles) in the air at the MPC level.

Determination of gasoline vapors in air, n = 5, P = 0.95

Table Introduced, mg / m ³ Found, mg / m ³ S _r fifty 45.6 ± 2.88 2,5 60 56.6 ± 2.52 2,3 70 68.9 ± 2.35 2,4 80 78.3 ± 1.85 1.8 90 89.2 ± 1.08 1,5

n is the number of definitions;

P is the confidence probability;

Sr is the error.

Claims (1)

A method for determining gasoline vapors in air, characterized in that the electrodes of the piezoelectric quartz resonator of the AT-cut with an oscillation frequency of 9 MHz are modified with a solution of β-cyclodextrin in ethanol so that the film mass after exposure of the piezosensor in an oven at 60 ° C was 20 μg, then for 2 min the analyzed air containing gasoline vapors was blown into the cell through a filter cartridge for 2 minutes, placing the prepared piezosensor t into the detector and included in the circuit of the high-frequency quartz oscillator, the analytical signal is recorded in the form of the oscillation frequency of the quartz plate of the piezosensor when thermodynamic equilibrium is established in the sorption system, as evidenced by the constant frequency of the oscillation of the piezosensor in time, a calibration graph is constructed by which the concentration of gasoline vapors is found in the air.