SU1557519A1 - Method of determining the content of nitrates in plant-growing products of cruciferae family - Google Patents

Abstract

The invention relates to the food industry, in particular to the analysis of the quality of plant products. The aim of the invention is to improve the accuracy of the method. The method allows to separate impurities that interfere with the determination of nitrates in extracts of cruciferous plant products, by treatment with a strong oxidant (a mixture of potassium permanganate and sulfuric acid) in combination with subsequent destruction of excess potassium permanganate by hydrogen peroxide, which also affects the potential of the electrode system in the test solution. 1 tab.

Description

The invention relates to the food industry, in particular to methods for analyzing the quality of plant products.

One of the food contaminants is nitrates, which can cause hemoglobinemia in humans and animals and the formation of carcinogenic N-nitrosamines.

The aim of the invention is to improve the accuracy of the method.

The method is carried out as follows.

10 g of potassium aluminum dyes are introduced into a volumetric flask with a capacity of iOOO ml and dissolved in distilled water. Then 1.0 g of manganic acid potassium is added and the same amount of concentrated sulfuric acid is placed there. The resulting mixture was shaken and the solution was made up to the mark with distilled water.

The analysis of nitrates in samples of cruciferous plant growing products involves the extraction of nitrates from the sample with an extracting solution by treating the product at room temperature for 10 minutes with stirring. It was taken into account that the extracting solution includes sulphates (potash alum), which are necessary to create a certain concentration of sulphate ions in the solution, which creates the necessary ionic strength of the solution, and this ensures the stability of the background potential required for a stable electroU1 works

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yes, and it has been established that the alum concentration is between 0.5 and 1.5% is optimal.

Cruciferous plant products contain impurities, including sulfur compounds with an oxidation state of 2, which affect the potential of the electrode system, significantly overestimating the results of the analysis. In order to eliminate this effect, interfering impurities are oxidized to compounds that do not affect the ionometric determination of nitrates. Of the oxidizing agents used (perchlorate, chromates, and DR.), Potassium permanganate with sulfuric acid was the best.

However, the MnO4 ion has a high selectivity coefficient relative to the nitrate-selective electrode, therefore an excess of MnO ions is converted into Mn ions by treating the solution with hydrogen peroxide in a sulfate medium, as a result of which the influence of nitrates in cruciferous plant raw materials is completely excluded. .

The treatment of excess permanganate is carried out until the solution is light colored, which indicates the absence of a colored MpOx ion.

For carrying out the method, 50–200 µl of a concentrated solution of 30% hydrogen peroxide is used. This amount allows for complete removal of the Mp04 ion, but does not significantly change the volume of the analyzed solution.

After the bleaching, the concentration of nitrate ion is measured using electrodes with a nitrate function.

Based on the measurements of the potential, the concentration of nitrate ion in the analyzed sample is calculated according to the formula 1:

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1000-N

- concentration of nitrate ions in

the analyzed sample, mg / kg; - the volume of the extracting solution, ml;

- mass fraction of water in the sample,%; - sample mass, taken by dp analysis

for, g; water density, g / ml; nitrate concentration in the extract, mol / l;

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Q

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M is the molar mass of the nitrate ion, g.

When excess potassium permanganate is added with respect to sulfuric acid, the equilibrium of the redox reaction shifts, resulting in incomplete purification from impurities.

Violation of the ratio of the amount of a mixture of potassium permanganate and sulfuric acid to the volume of the extracting mixture leads to a change in the ionic strength of the analyzed solution, which reduces the accuracy

Moreover, when the sample is kept for 5-10 minutes, the impurities are completely oxidized, and a further increase in the exposure time does not affect the readings of the ionometer, but increases the test time.

Example 1 o A sample of white cabbage, a member of the cruciferous family, is ground. The resulting mass is thoroughly mixed, a sample of 10.0 g is taken, placed in a beaker, 50 ml of an extracting solution containing 0.5% (0.25 mg) of potassium alum, 0–35% (0.17 ml) of sulfuric acid, and such the same amount of potassium permanganate, and stirred for 10 minutes, after which 4 drops (0.12 ml) of 30% hydrogen peroxide are added until the solution is discolored. In the resulting mixture, the potential of the electrode system in the ion meter is measured using a nitrate selective electrode, the concentration of which is determined by the concentration of nitrates n ruled sample according to the above formula

PRI me R 2o Same as in example 1, but turnips (crucifers) were used as the sample to be analyzed. The results of the analysis of nitrates in turnips are presented in the table.

Example 3. Same as in Example 1, but a potato was taken as the sample to be analyzed, which does not belong to the cruciferous family. The results of the analysis are presented in the table „

Example 40 As in example 1, but the extracting mixture contains 10 times less potassium permanganate than in example I, when determining the nitrates in the analyzed sample, overestimated results were obtained,

Example 5, Same as in Example 1, but the extracting mixture contains 515.

Lives 5 times less sulfuric acid than in example 10 When determining the nitrates in the analyzed sample, overpriced results were obtained

Example 6. Same as in example 1, only the treatment of the crushed sample with the extraction of the mixture containing potassium permanganate and sulfuric acid is carried out for 3 minutes. When determining the content of nitrates, their number is overestimated by 2 rads compared with example 10

Example. Same as in example 1, only the treatment of the crushed sample with an extracting mixture containing potassium permanganate and sulfuric acid is carried out for more than 10 minutes. A stable reading of the ionometer was detected in the determination of the nitrate content, which does not change with an increase in the exposure time.

The results of the analysis are presented in the table.

As can be seen from the table, the results of the analysis of nitrate in cabbage (Example 1) are in good agreement with the result of the photometric method, while the results obtained by the ionometric method without oxidizer treatment are overestimated by more than 5 times.

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Similar results were obtained when analyzing samples of another representative of crucifers - turnips. For potatoes that do not belong to this family, the results obtained by the three methods are almost the same (example 3).

Claims (1)

U Formula of inventions Method for determining the nitrate content in cruciferous plant crop products, including grinding the sample to be analyzed, extracting nitrates with an aqueous solution of aluminum-potassium alum, measuring the potential of the electrochemical system using ion-selective electrodes with nitrate function and quantifying nitrates in the sample being analyzed, characterized by method, the extraction of nitrates is carried out with a solution containing additionally potassium permanganate and sulfuric acid, taken In equal amounts, the potassium alum takes in the amount of 0.5-1.0% of the total solution, and before measuring the potential, the extract is kept under stirring for 5-10 minutes and treated with hydrogen peroxide until bleaching. five 0 five 0