SU735982A1 - Method of determining nitrate ions - Google Patents

Description

The invention relates to analytical chemistry, in particular, to the graphic definition of the nitrate ion, and can be used in various areas of the national economy related to the control of nitrate ion production, for example, in agriculture. At present, nitrate-ion in a phosphate-containing chloride chloride is determined by the participation of N0% in nitration reactions of some aromatic compounds with a mixture of nitrate and sulfuric acid being analyzed. And the sensitivity of determination of 2.10 M. for the analysis of fertilizers of soil and other systems by potentiometric titration with a solution of ferrous iron as a reducing agent in a medium of condensed phospho Н H 2 acid. The method makes it possible to determine nitrates in the presence of oxidizing agents and colored x substances. However, the potentiometric titration method itself is very time consuming. and therefore unsuitable for mass determinations, since it requires multiple measurements. The closest in technical essence and the achieved result to the proposed invention is the method of determining nitrate ions, based on the reaction of nitration of nrt - with reagents from the class of aromatic phenols, the most widespread of which received 2, B-xylenolc. Sensitivity of determination 2.1O M. Progress of analysis. In a dry flask, 6 ml of concentrated sulfuric acid, 1 ml of O, 1 m solution, 2,6-xc1-shanol in glacial acetic acid, 3 ml of the analyzed aqueous solution are placed, the flask is placed in a water bath for 15 minutes and then cooled to room temperature temperature Transfer the solution to a dry polarographic cell, pass nitrogen, purified from oxygen, for

10 minutes, and record the cathode wave in the limit from –O.to -0.7 V (with merculate electrode).

This method has a lack of sensitivity, is difficult to implement and time consuming.

In addition, with this sequence of addition of the components — sulfuric acid, the reagent, the sample — the pepper, the nitration process prriscod the proximate sulfate reagent, competing with nitration, which underestimates the results by nitrate ion in the sample by 2.5 times.

The purpose of the invention is to increase the sensitivity of determining and simplifying the application, i.e., a method suitable for mass determination of nitrate ion.

This is achieved by determining that the nitrate ion is determined; polarographically by the participation of N0) in the reaction to nitration of the following aromatic phenols: thymol - ° C and - naphthol, phloroglycine or resorcinol using a mercury drip-. During the nitration reaction, sulfuric acid is introduced after the addition of the reagent: the titration process is carried out with cooling.

The proposed compounds are 10 to 20 times more sensitive than the currently used 2,6-xylenol,

The studies were carried out on a LP-7 polygraph with a mercury dripping electrode. Capillary characteristic 1.25.

To 2 ml of the analyzed aqueous solution was added 0.5 ml of OD of a solution of one of the reagents in acetic acid: thymol, cC-naphthol, -naftol, phloroglycine or resorcin. The contents are stirred, then 2.5 ml of the terminated sulfuric acid is added, stirred again. The reaction mixture is cooled to room temperature in a stream of water or snow, then placed in a polarographic cell, washed with water, and after 8-10 minutes of flowing a stream of nitrogen, purified from oxygen, is recorded; cathode wave from -0.2 to -0.7 V relative to p5tential bottom pfyTH. At the same time, a stream of nitrogen is passed into the next analyzed solution. To determine the nitrate ion, a calibration plot of the dependence of the diffusion current of the reduction of the corresponding nitro compound on the height of the cathode is constructed. The coefficient of variation does not exceed 6%,

Note:

1.Technical resorcinol gives a clearer cathode wave than the purified one;

2.o4-naphthol and phloroglycine of all these compounds give the clearest cathode wave,

The table for comparison shows some indicators of the nitro derivatives of the proposed reagents.

Claims (3)

Potential of half-wave reduction -0.40 -0.41 nitro compounds, V Sensitivity 2-10 determinations, gs / l Diffusion current of restoration Inhibits for 2 10g / l, A 48.943.7 0.415 -0.45 -O , 455 2 "10 2-10 2MO 8.946,461.1 The proposed method has the following advantages: a) the method is more sensitive (10-2O times) with the same selectivity; , b) ease of analysis - absent in d on a ban; . c) speed of analysis - no more than 4 minutes for cell preparation and cathode wave recording. Example. The definition of nItrat-io in the soil. 3 g of podzolized black earth soil is mixed with 15 ml of 0.05% Kg 56 for 3 minutes. Not filter, add 0.5 ml OD of a solution of thymol in acetic acid to the extract. The contents are stirred, 2.5 ml of concentrated is added. mix again. The reaction mixture is cooled in a stream of water or snow to room temperature, placed in a cell washed with water, and a stream of nitrogen purified from oxygen is passed through for 8-10 minutes. Then, the cathode wave is recorded in the range from 0.2 to 0.7 V. At the same time, nitrogen is passed through the next solution. Concentration is determined. NOj by adding a standard solution to the sample to be analyzed. The sensitivity of the method is 0.8 mg / kg of soil. The N0 content in different samples of podzolized chernozem is 1.42-229 mg / kg. The error of determination in comparison with the standard - disulfur-null method does not exceed 2.5%. The cell preparation and wave recording time is not more than 4 min. By using this method, labor productivity will increase 2.5-fold compared to the disulfophenol method. . The determination can be carried out for & es, turbid and colored solutions. The ions of the periodic system, which are close in terms of the reduction potential iNOj, can interfere with the determination. Or-i, with respect to fNOr - O, 365 µg / ml of non-O4 2, is prevented by a thousand-fold excess of Cu, Co. several thousand times the excess RO (which is very important in the agrochemical analysis of the soil), in comparable amounts of Cu (in the agrochemical analysis practically does not interfere), 46 is a multiple of the excess of re (I µg / ml), 4O is the multiple of the excess of IP, Mp ( 14.5 µg / ml), but Fe Fe, Ip2-Ig7, interferes in greater amounts (they can interfere with the agrotechnical analysis of the soil). NOg interferes, but in the soil it is present in negligible 826 quantities. The proposed new order of addition of the reagent (for polygraphic and and not for cjiuHTHTH nitration) complement1; but it increases the sensitivity of the method, approximately 2 times. Change the reaction medium with / oTo. up to SU / 0. Ultimately, it increases the detection sensitivity: the value of 3 (diffuse recovery fOK) decreases in this case by 1.08, and the number of samples increases by 1., 34 times. . For all the samples, the coefficient of recalculation of the values according to the calibrated graph was calculated for the data characteristics of the vrt capillary - 1.25 for the content of the soot ions (KD) of the calculation. The method of adding a standard solution to the analyzed sample was used. The average coefficient obtained is used to calculate all soil samples. The formula for calculating I / - C Y7. h ..- h is the conversion factor for a given soil — the height of the recovery wave is 0.210 g-1 / l N0; - changing the height of the recovery wave on this background; - recovery wave height for a given soil h j for a given wave height with the introduction of a standard solution of 0.2.10 G / -I / L NOl. Claims 1. A method for determining nitrate ions, comprising the nitration of compounds belonging to the class of aromatic feols with a nitrating mixture consisting of centric sulfuric acid and nitate ion, followed by a voltammetric analysis of the resulting nitro compound, which the purpose of increasing the sensitivity of the definition and simplified. analysis, the quality of the reagent from the class of aromatic phenols used thymol, naphthol, fluoroglycerol, or resorcinol, 7735982b and when carrying out the sulfur-1 nitration reaction. K.Hondu, S.KUKucbbnftuig.of the The acid is added after the addition of Chem. wasps p xGarap, reagent. 34. No. 4. 1961. 2. The method of clause 1, clause 2 of the copyright certificate. CCH yi AI with the fact that the process of nitration s according to application No. 2312389 / 26-29, from cooling during cooling 06,01,76. , „ .. 3. Am.Harttev. „AnafttSources of information, h -UcaiOvevnisi vV taken into account in the examination number 35, 686. 1963 (prototype).