Abstract
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 NOxfrom different samples ensuring removal of potential interfering agents. The method provides over 95 per cent mean recovery with nearly 3 per cent 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.
Highlights
For present investigation incubation of test samples in boiling water bath for maximal limit of ten minutes, range 3 – 10 (Mir, 2008), was found advantageous as it obviated any interference from lower levels of nitrite, < 0. 5 ppm N, and caused 97.4 ± 0.6 per cent loss in diazotization of nitrite at higher levels, 0.75 to 3.0 ppm N (n=15), compared to values observed at room temperature
This implies that urea treatment may not be required at low nitrite levels while employing maximal limit of incubation period for acid reduction
The present study has revealed mean concentrations of nitrate and nitrite highest, ca.185 to 270 and 0.3 to 0.7, in radish, spinach and carrot, intermediate, ca. 40 and 0.3, in potatoes, and lower, ca. 11 and < 0.1, in cabbage
Summary
The experiments were carried out at an ambient temperature of 20.6 ± 0.7 0C. Treated sample extracts were each added 9 mL of acetic acid solution, and a scoopful, ca. Each 5 mL filtrate was added 0.2 mL NEDA, and color monitored at 540 nm after 20 minute standing. Water blank and nitrate standards, 1 and 3 ppm as N, were subjected to identical treatments. The concentrations of nitrate and nitrite in the samples were calculated in terms of simultaneously processed standards:. X = Concentration of the analyte in the original sample, ppm N. B = Concentration standard as μg N. D = mL sample extract used for the assay. E = Concentration of sample extract, g or mL original sample per mL sample extract
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