RU2265828C1 - Method for photometric determination of nitrite in liquid medium - Google Patents

Abstract

FIELD: analytical chemistry.

SUBSTANCE: method involves interaction of nitrites with composition of chromogenic analytical reagents and the following evaluation of nitrite concentration by calibration plot showing dependence of optical density of solution and the concentration of nitrites. Method involves using 3-hydroxy-7,8-benzo-1,2,3,4-tetrahydroquinoline in combination with 2-aminobenzoic or 4-aminobenzoic acid, or sulfanilic acid, or sulfanilamide as chromogenic analytical reagents. Reagents are fixed on paper vehicle that is placed in solution for photometry across the light flow. Method provides reducing analysis time, simplifying and improvement of conditions in carrying out tests.

EFFECT: improved method for determination.

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Description

The invention relates to analytical chemistry, in particular to methods for determining the concentration of nitrites using a photocolorimeter, and can be used for the quantitative determination of nitrites in aqueous media, as well as in wastewater generated during the neutralization of rocket oxidizers based on nitric acid.

Methods for the photometric determination of nitrites in solutions are based on the formation of azo compounds (I. M. Korenman. Photometric analysis. Methods for the determination of organic compounds. M: Chemistry, 1975, p. 58). The disadvantages of these methods include the need to prepare solutions of analytical reagents and the bulkiness of the photometers used.

The closest analogue of the method for photometric determination of nitrite by technical essence is the photometric method based on the reduction of nitrite with sulfanilic acid, 1-naphthylamine or NED, and the subsequent photocolorimetric determination of the colored product formed in the solution on a photometer (prototype). The total analysis time is 40 minutes. (Unified methods for researching water quality. Part 1. Methods of chemical analysis of water. // Meeting of the heads of water management bodies. M: Publishing House of Council for Mutual Economic Assistance, 1987, pp. 672-677).

The main disadvantages of the known photocolorimetric method are the long duration of the analyzes, due to the need to prepare standard solutions of analytical reagents before analysis, the use of toxic reagents such as carcinogenic 1-naphthylamine and dermatose alkyl derivatives of 1-naphthylamine.

The aim of the invention is to reduce the time for analysis, simplification and improvement of test conditions, as well as the possibility of working in off-laboratory, in particular field conditions using ready-made portable means of photometric analysis: photometers and analytical reagents mounted on solid-phase beds that can be stored for a long time; extension of the intervals of the determined contents while maintaining the sensitivity of the determination.

This goal is achieved by the fact that the proposed method for the photometric determination of nitrites in a liquid medium, including their interaction with the composition of chromogenic analytical reagents and the subsequent assessment of the concentration of nitrites according to the calibration graph of the optical density of the solution versus concentration, according to the invention, 3-hydroxy 7,8-benzo-1,2,3,4-tetrahydroquinoline in combination with 2-aminobenzoic, or 4-aminobenzoic, or sulfanilic acid, or su fanilamidom fixed on the paper, which was placed in the solution across the photometric light flux.

A wide range of detectable concentrations at a sufficiently high sensitivity is shown in Figs. 1-4.

Figure 1 shows the dependence of optical density (A) on wavelength (λ, nm) for reagent indicator paper (RIB), including 3-hydroxy-7,8-benzo-1,2,3,4-tetrahydroquinoline (GBTH) in combination with 4-aminobenzoic acid (PABA) (RIB I), 2-aminobenzoic (anthranilic) acid (AK) (RIB II), sulfanilic acid (SC) (RIB III), or sulfonamide (RIB IV) at a nitrite concentration of 10 mg / l KFK-2MP photocolorimeter, 0.1 cm cell thickness.

As can be seen from Figure 1, the RIBs are suitable for operation on a photometer with a green radiation source.

Figure 2 shows a calibration graph of the photometric determination of nitrites in the concentration range from 0.5 mg / l to 20 mg / l using RIB based on GBTH in combination with AK. Determination time 10 min. The wavelength of the filter is 490 nm. The thickness of the cell is 0.1 cm.

Figure 3 shows a calibration graph for the photometric determination of nitrites in the concentration range from 0.125 mg / l to 1 mg / l using RIB based on GBTH in combination with AK. Determination time 10 min. The wavelength of the filter is 490 nm. The thickness of the cell is 0.5 cm.

Figures 2 and 3 confirm a wide range of detectable nitrite contents from 0.1 to 20 mg.

Figure 4 presents the x-ray structural analysis of the isolated reaction product of nitrite with reagents on RIB; its molar absorption coefficient of the product is 31,000, which confirms the high sensitivity of the RIB.

The following is an example implementation of the claimed method.

Stage 1. Obtaining an indicator element - reagent indicator paper (RIB).

To create an indicator element - solid-phase carrier of reagents using reagents:

3-hydroxy-7,8-benzo-1,2,3,4-tetrahydroquinoline (GBTH), mp 156 ° C;

2-aminobenzoic acid (AK), h, according to GOST 11121-65;

4-aminobenzoic acid (PABA), h, according to MRTU 6-09-6315-69;

sulfonamide, white streptocide (BS), h, according to GOST 8894-74.

As a solid-phase carrier, base paper is used for express tests of brand I with a specific surface of 80 g / m ² .

To substantiate the significance of the distinguishing features, RIB II samples with different reagent contents were prepared, which were used to determine the concentration of nitrites in solutions (Table 1).

RIB II is made by applying reagents: HBTH, AK, citric acid, tartaric acid, oxalic acid on a base paper for rapid tests of the reagents (Table 1). RIBs are cut into strips and packaged in sealed canisters or plastic bags. For RIB I, III, IV, the same amounts of PABA, SC, or BS are used instead of AK.

Table 1.
Solid Reagent Content Components,% mass Rib Samples II No. 1 Number 2 No. 3 Number 4 GBTH 0.22 0.3 0.44 0.5 AK 0.7 1,0 1.4 1,5 lemon acid 0.9 1.3 1.8 2.0 wine acid 0.85 1.25 1.7 2.0 oxalic acid 0.4 0.6 0.8 1,0

Stage 2. Construction of calibration graphs for the determination of nitrites.

The optical density (A) of the indicator element is measured on a KFK-2MP photoelectric colorimeter in 0.1 cm and 0.5 cm cuvettes. Tests are carried out on diluted standard solutions of sodium nitrite according to GOST 4212-62 (1.5 g per 1000 ml of water ), given concentrations of nitrite ions (0.125; 0.5; 0.8; 1; 2; 4; 5; 10; 20 mg / l). The indicator element is contacted with the sample directly in a 0.1 cm and 0.5 cm thick cuvette, for which, using pipettes with a capacity of 1-2 ml according to GOST 20292-74, the same amount of solution is introduced into the cuvette, and then the indicator element is placed across the cuvette luminous flux and measure the optical density.

Measurement of the optical density (A) of solutions with the reaction product of nitrite with RIB (Figure 4) is carried out at different wavelengths of optical filters (400 nm, 440 nm, 490 nm, 540 nm, 590 nm, 670 nm) in order to determine the optimal maximum wavelength absorption. The optimal wavelength of the filter is 490 nm, at which the absorption spectra have maxima (Fig. 1, RIB I, II, III, IV).

On standard solutions of sodium nitrite, calibration graphs of photometric determination of nitrites using RIB are built at a wavelength of 490 nm in the range of concentrations from 0.5 mg / l to 20 mg / l with a cell thickness of 0.1 cm (Figure 2); in the range of concentrations from 0.125 mg / l to 1 mg / l with a thickness of the cuvette of 0.5 cm (Figure 3).

The obtained calibration graphs are an integral part of the method and are stored together with indicator elements.

Stage 3. Determination of nitrites in technical solution.

Before photometric measurement, a simple test of the analyzed solution is carried out by immersion in it for 1 s of a colorless indicator element. The appearance of color indicates the presence of at least 0.5 mg / l nitrite.

After that, the analyzed solution (sample) using a pipette with a capacity of 1-2 ml according to GOST 20292-74 is introduced into the cuvette, then the indicator element obtained in Example No. 1, sample 2 of Table 1, is lowered into the cuvette, held for 10 minutes and measured optical density of the indicator element on the photometer. The control solution is distilled water with the same indicator element. The readings of optical density (A) are taken, and the nitrite concentration is determined from the calibration curve.

Option 2 stages 3. Determination of nitrites in natural and waste waters.

Take 0.6 ml (for a cuvette with a thickness of 0.1 cm), 2.5 ml (for a cuvette with a thickness of 0.5 cm) of the analyzed solution and place it with a pipette into the cuvette. Then, the RIB band is placed in the cuvette; after staining the RIB band, the readings of the KFK-2MP photometer are determined: optical density at 490 nm and the nitrite concentration is found from the calibration graph.

In the same way, nitrite is determined using a UNIFOT-LUM 8C-120 luminometer photocolorimeter. In this case, 1 ml of sample is added to the cuvette, and the readings of the device are measured with an LED with a wavelength of 505 nm.

The results of the determination of nitrites are presented in table.2.

For reagent pairs: GBTH with PABA, SC and BS, standard deviations increase in the order of mention by 3-10%.

Thus, the use of the invention will reduce the analysis time by 3-5 times, improve the test conditions, and also determine the concentration of nitrites in the field using portable tools and devices in a wide concentration range of 0.1 mg / l -20 mg / l at achieving sensitivity at the level of maximum permissible concentrations for drinking water (0.1 mg / l), water bodies (1 mg / l), fisheries basins (0.2 mg / l).

Claims (1)

A method for the photometric determination of nitrites in a liquid medium, including their interaction with a composition of chromogenic analytical reagents and a subsequent assessment of the nitrite concentration according to the calibration graph of the solution optical density versus concentration, characterized in that 3-hydroxy-7.8-benzo is used as chromogenic analytical reagents -1,2,3,4-tetrahydroquinoline in combination with 2-aminobenzoic, or 4-aminobenzoic, or sulfanilic acid, or sulfanilamide, mounted on a paper carrier, which is placed in a photometric solution across the light flux.

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