Extraction of NOx and Determination of Nitrate by Acid Reduction in Water, Soil, Excreta, Feed, Vegetables and Plant Materials

Different methods are available for extracting NOx from different samples. A judicious combination of lead acetate, sodium hydroxide and magnesium chloride has been devised to enable extraction of NOx from different samples ensuring removal of potential interfering agents. The method provides over 95 percent mean recovery with nearly 3 percent accuracy and precision. Nitrite is determined by Griess reaction, and removed from samples by urea treatment to obviate any interference by nitrite in nitrate determination. Nitrate is determined by acid reduction method with minimum detection limit 0.5 ppm as N. The methods have been applied to selected environmental samples including food materials and excretory products. The average nitrate levels (as ppm N) found in water (0.8), soil (9), human urine (43), sheep excreta (2654), chicken feed (29), radish (270), spinach (222), carrot (194), potato (41), cabbage (11), tomato (2), Bermuda grass (175) and morning-glory leaves (576) have been within safe and documented limits. The average levels of nitrite, as ppm N, have generally ranged from 0.04 to 2.1 with highest content, 13, in sheep fecal matter. The protocol is intended for general use in environmental analysis, toxicological investigations and risk assessments.