METHOD OF ASSESSING NITROGEN IN BIOLOGICAL SAMPLES Russian patent published in 2000 - IPC

FIELD: analytical methods in agriculture and food industry. SUBSTANCE: invention is designed for use when diagnosing plant nutrition and also when controlling quality of agricultural produce and consists in quantitative determination of nitrogen in natural and industrial products. Nitrogen in biological samples is determined as follows. Hydrogen peroxide and sulfuric acid are first added to sample. The latter is heated until white smoke appears and decoloration is completed. After that, distilled water and (in which novelty consists) borate buffer are added. Mixture is neutralized with NaOH. Manganese, sodium hypochlorite, potassium iodide, and sulfuric acid solutions and then starch are added to mixture, after which mixture is titrated to decoloration. The same procedure is repeated with reference sample and nitrogen content is determined from following equation: X = (0,1166(V_o-V₁)•*100*100%/m,V₂, in which V_o is volume of sodium thiosulfate solution consumed for titration of reference sample, ml; V₁ the same for titration of biological sample, ml; V₂ volume of sol solution of biological sample, ml; m weight of biological sample, mg; 0.1166 is number of mg of nitrogen corresponding to 1 ml of 0.025 N sodium thiosulfate; and 100 is initial volume of sol solution of biological sample, ml. EFFECT: reduced duration of analytical procedure, improved reproducibility and accuracy.