RU2319958C1 - Method of determining microconcentrations of ammonia vapors in air - Google Patents

Abstract

FIELD: analytical methods.

SUBSTANCE: invention relates to analytical chemistry of inorganic compounds and comprises providing chemisorbent, filling test device therewith, exposing it to ammonia vapors, registering analytical signal with a time range 10-15 sec, and finding ammonia concentration from calibrated graph. Test device represents quartz piezoelectric resonator with its electrodes modified by sulfosalicylic acid solution so that mass of the film formed after drying-mediated removal of solvent in drying oven at 40-50°C for 15-20 min at horizontal arrangement of resonator is 10-15 μg.

EFFECT: increased sensitivity, accuracy, rapidity, and selectivity of analysis.

2 dwg, 1 tbl

Description

The invention relates to analytical chemistry of inorganic compounds and can be used to determine the microconcentration of ammonia vapor in air and a gas mixture of any composition.

The closest in technical essence and the achieved effect is a method for determining the concentration of ammonia vapor using indicator tubes based on mercury (II) nitrate [Yu.A. Zolotov, V. G. Amelin // Test analysis methods. - M .: Chemistry, 2002, - 290 p.].

The disadvantage of the existing method is the toxicity of the sensitive filler reagent (mercury salt), a high detection limit in determining microconcentrations of ammonia vapor in the gas phase, the duration of the analysis, the need for air aspiration, the subjectivity of fixing the analytical signal, the dependence of the length of the colored zone on the inner diameter of the tube, the rate of air leakage , the fuzziness of the border of the colored region due to erosion of the chemisorbent. The method is characterized by high errors, which is associated with different densities of the indicator packings and uneven media impregnation.

An object of the invention is to develop a method for determining ammonia vapor in air in the concentration range of 0.01-10 mg / m ³ using a piezoelectric crystal transducer with a thin film coating, characterized by high sensitivity, with low detection limits, accuracy, expressivity and selectivity of analysis, measurement objectivity and decision making, the safety of the reagents used.

.The stated technical problem is achieved by the fact that in the method for determining the microconcentrations of ammonia vapors in air, including the preparation of chemisorbent, filling it with a test device, exposure in air, determining the concentration of ammonia, it is new that a piezoelectric crystal is used as a test device, the electrodes of which modify by applying a solution of sulfosalicylic acid on them so that the mass of the sorbent film after removing the solvent by drying in an oven at a temperature of 40-50 ° C for 15-20 min and the horizontal arrangement of the resonator was 10-15 μg, the change in the frequency of oscillations of a piezoelectric crystal resonator with a film (sensor) in a gas mixture or air with ammonia was recorded for 10-15 s, from which the ammonia concentration was found using a calibration graph

.

The technical result of the invention is to develop a method for determining microconcentrations of ammonia vapors in air due to a chemical reaction on the coating surface, expanding the base of existing modifiers for determining microconcentrations of ammonia in air, reducing the total analysis time, reducing detection limits and relative error, significantly increasing the selectivity of determination and objectivity of measurements and decision making, increase of expressness of measurements and safety of preparations measuring device to work.

.Figure 1. - Calibration graph for determining the content of ammonia vapor by changing the frequency of oscillations of a piezoelectric crystal resonator with a film of sulfosalicylic acid on the electrodes

.

Figure 2. - Sorption activity of the sulfosalicylic acid film to compounds of various nature: 1 - ammonia, 2 - water, 3 - ethanol, 4 - aniline, 5 - acetone, 6 - methyl ethyl ketone, 7 - phenol, 8 - hydrogen sulfide.

The method for determining the microconcentration of ammonia vapor in the air is as follows.

, который строят по стандартным газовым смесям, находят концентрацию его в анализируемой пробе воздуха (фиг.1).A solution of sulfosalicylic acid is applied to the electrodes of the piezoelectric crystal so that the mass of the sorbent film after removing the solvent by drying in an oven at a temperature of 40-50 ° C for 15-20 minutes and a horizontal arrangement of the resonator is 10-15 μg. A prepared resonator with a film is placed in a closed detection cell and the initial (“zero”) response of the sensor — the oscillation frequency — is recorded. Then, a sample of air containing ammonia vapors at the level of microconcentrations (0.01-10 mg / m ³ ) is injected into the cell with a syringe. Register with a frequency meter or using a computer a change in the frequency of oscillations of a piezoelectric crystal resonator with a film (sensor) in a gas mixture or air with ammonia for 10-15 seconds. Calculate the change in the oscillation frequency of the sensor with the introduction of ammonia vapors and according to the calibration graph

, which is built on standard gas mixtures, find its concentration in the analyzed air sample (figure 1).

To assess the sensitivity and selectivity of determining a piezoelectric crystal with a film of sulfosalicylic acid (sensor) is exposed in pairs of test compounds (figure 2). The sulfosalicylic acid-based sensor exhibits an extremely high sorption affinity for ammonia with almost complete sorption inertness to other compounds.

The positive effect of the proposed method is achieved due to the fact that sulfosalicylic acid is characterized by selectivity and specificity for ammonia vapors, due to the high acidic properties of the sulfo group, which, in turn, contributes to the chemical reaction of the sulfo group with the formation of sulfosalicylic acid ammonia, then a reversible interaction on the carboxylic acid and hydroxyl groups.

, который строят по стандартным газовым смесям аммиака.The concentration of ammonia vapor is found on the calibration curve

built on standard ammonia gas mixtures.

All measurements are carried out in a closed monosensor detection cell with injection injection of the sample in static conditions.

The method is illustrated by the following example.

Example

(фиг.1). Вкалывают в детектор шприцем анализируемую пробу воздуха, содержащую аммиак. Фиксируют частотомером или с помощью компьютера изменения отклика сенсора (частота колебаний) в течение 10 с. Рассчитывают изменение частоты колебаний сенсора (аналитический сигнал) при введении паров аммиака и по градуировочному графику (фиг.1) находят концентрацию его в анализируемой пробе воздуха.A solution of sulfosalicylic acid is applied using a syringe with two syringes of ethylene-fat-free electrodes of an AT-piezoelectric quartz resonator with a natural oscillation frequency of 8-10 MHz and the free solvent is removed in an oven for 20 min at a temperature of 45 ° C, placing the resonator strictly horizontally in the holder. The mass of the film after drying and cooling is 15.5 μg. A prepared resonator with a film (sensor) is placed in a closed detection cell and the initial (“zero”) response — the oscillation frequency — is recorded. The drift of the "zero" line after drying is ± 3 Hz / min. With a larger deviation, the film resonator is re-dried. Then, standard gas-air mixtures with a known concentration of ammonia (0.01-10 mg / m ³ ) are successively injected into the detection cell with a syringe. Register with a frequency meter or using a computer a change in the frequency of oscillations of a piezoelectric crystal resonator with a film (sensor) in a gas mixture or air with ammonia for 10-15 seconds. Calculate the change in the frequency of oscillations of the sensor with the introduction of ammonia vapor and build a calibration graph in coordinates

(figure 1). An analyzed air sample containing ammonia is injected into the detector with a syringe. The frequency response or using a computer is used to record changes in the sensor response (oscillation frequency) for 10 s. Calculate the change in the oscillation frequency of the sensor (analytical signal) with the introduction of ammonia vapors and according to the calibration curve (Fig. 1) find its concentration in the analyzed air sample.

Without updating films, analysis of 10-12 samples is possible, including calibration mixtures. After that, the film is easily washed off with water and re-applied to the same transducer.

When implementing the method for determining the microconcentration of ammonia vapors in air, the detection limit of ammonia in the gas phase is reduced; reproducibility of measurements increases; eliminates the interfering effect of related components in the analysis of ammonia vapor; expressivity and selectivity of determination increase; no toxic reagents are used to prepare the device for operation.

The method is feasible.

Comparative characteristics of the proposed method and prototype are shown in the table.

As can be seen from the example of the table and FIGS. 1-2, a positive effect on the method for determining the microconcentrations of ammonia vapors in air is achieved by using a piezoelectric crystal transducer modified with a solution of sulfosalicylic acid as a test device by applying it to two electrodes, followed by drying, horizontally strengthening the resonator in the holder for 15-20 minutes at a temperature of 45-50 ° C, so that the mass of the sorbent film is 10-15 μg, the concentration of ammonia is found according to the calibration curve according to the resonant response and the film in an ammonia vapor, measured within 10-15 seconds.

The developed method allows to determine ammonia in air at a concentration level of 0.01-10 mg / m ³ , reduce the total analysis time (up to 1 min). The express method, easily feasible, highly selective, is applicable for determination of ammonia vapors in the air of various objects and complex mixtures of gases.

A change in the nature of the sorbent, the method of forming the modifier film, the position of the resonator, temperature and time during drying, as well as its mass does not allow a uniform thin-film coating to form on the surface of the piezoelectric crystal and, as a result, leads to a decrease in sensitivity and a high error in the determination of ammonia. Changing the time of registration of the analytical signal of the sensor during sorption leads to high errors in constructing a calibration graph and quantitative estimation of ammonia vapor in the gas phase.

The proposed method in comparison with the prototype allows you to:

- reduce the detection limit of ammonia in the gas phase by 10 times;

- increase the reproducibility of the analysis by 5 times;

- increase the reproducibility of the stage of formation of the sensitive layer of the sorbent 5 times;

- eliminate the interfering effect of related components in the analysis of ammonia vapor;

- reduce the total analysis time by 5 times;

- increase the selectivity of determination;

- increase the objectivity of measurement and decision making;

- Do not use toxic reagents to prepare the device for operation.

Table Comparative characteristics of the proposed method and prototype for the determination of microconcentrations of ammonia vapor in the air Criteria Way Prototype The claimed Range of detectable concentrations 4-30 mg / m ³ 0.01-10 mg / m ³ Sensitive Toxicity + - Air sampling device + + The need for pre-aspiration + - Regeneration and reusability - - Possibility of reuse when updating the surface of the sensitive layer - + Disturbing effect of components amines, water vapor not found The cost of one determination (excluding the cost of auxiliary equipment) 400 p. 50 p. The subjectivity of determining concentrations + - Difficulty interpreting the results + - Analysis time 5 minutes 1 min The error of the stage of formation of the sensitive layer,% 17-20 5 Analysis error,% 5-10 2-3 Durability in the absence of ammonia vapors 2 months 8 months

Claims (1)

A method for determining microconcentrations of ammonia vapors in air, including the preparation of a chemisorbent, filling it with a test device, exposure to ammonia vapors, characterized in that a piezoelectric crystal resonator is used as a test device, the electrodes of which are modified by applying a sulfosalicylic acid solution on them so that the film mass the sorbent after removing the solvent by drying in an oven at a temperature of 40-50 ° C for 15-20 minutes and with a horizontal cavity was 10-15 μg, register and Changing the oscillation frequency of a piezoelectric crystal resonator with a film (sensor) in a gas mixture or in air with ammonia for 10-15 s, by which the ammonia concentration is found using a calibration graph

.

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