VALIDATION OF AN ENZYMATIC METHOD FOR NITRATES DETERMINATION FROM VEGETABLE PRODUCTS

Abstract

Nitrates and nitrites are natural components of soil, derived from mineralization of nitrogenous organic substances of vegetable and animal origin. Plants absorb nitrogen from soil, mainly as nitrates or ammonium forms. This paper presents the results of researches carried out to validate an enzymatic method for nitrates determination in vegetable products. Within this method, the nitrate is reduced by the reduced nicotinamide adenine dinucleotide phosphate (NADPH) to nitrite, in the presence of nitrate-reductase (NR). In the case of the enzymatic method for nitrates determination in vegetable products, the calibration curve achieved with 9 standard levels of nitrate ions (with three rehearsals for each one), in the range of concentrations 6 mg/L – 30 mg/L, beginning from origin and the linearity coefficient (r²), is 0.9999. For 10 vegetable samples grown in open field (egg plants, bell peppers, green peppers and onion) the average nitrate concentration of vegetable species varied in the range 27.91 mg NO₃^-/kg – 82.85 mg NO₃^-/kg, and repeatability was in the range 1.33 mg NO₃^-/kg – 1.50 mg NO₃^-/kg. The determination of nitrates in a cabbage sample, by three analysts, led to an average nitrate concentration of 107.42 mg NO₃^-/kg, relative standard deviation RSD(R), and the determined concentration is 0.81 %, and reproducibility is 2.45 mg NO₃^-/kg. The detection limit is 0.15 mg/L and quantification limit is 0.30 mg/L. In the case of onion sample grown in open field, the nitrates concentration was 55.5 mg NO₃^-/kg, and uncertainty was 0.68 mg NO₃^-/kg.