Nitrate and nitrite are extracted by shaking 2 g of air dried soil in 30 mL 0.01 M CaSO4for 15 minutes followed by filtration. The nitrate in the filtrate is measured on a Lachat Quikchem 8500 Flow Injection Analyzer. In this method, the nitrate is reduced to nitrite in a copperized cadmium column. The nitrite then reacts with sulfanilamide under acidic conditions to form a diazo compound. This in turn couples with N-1-Napthylethylenediamine dihydrochloride to form a reddish purple azo dye, which is measured colorimetrically at 520 nm. Nitrite is determined by the same process but without using the copperized cadmium column.
(Extraction: Ref. No. 2 & 3, Analysis: Ref. No. 4 & 5 - Method References)