"Nitrate testing has a long history. The most commonly used detection method, involving reduction of nitrate to nitrite, uses diazo chemistry developed in the 1950's. Ion selective electrodes for nitrate became available in the 1960's. Methods based on direct nitration of aromatic compounds such as salicylate and brucine became popular in the 1970's. The reduction of nitrate to nitrite using a Cu-Cd (copperized cadmium) reductant and nitrite detection by diazo chemistry and various nitration systems are probably the most widely used methods in analytical laboratories and field test kits. As early as 1971 , the enzyme nitrate reductase (NaR) was suggested as an alternative catalyst for the reduction of nitrate to nitrite. The enzymatic reduction method offers several advantages over the chemical reduction method: it is sensitive, since the catalyst is effective in small sample volumes; it is specific; and it can be formulated to utilize non-toxic reagents, which is a distinct advantage over the chemical reductant methods." (Campbell E. R., Corrigan J.S., Campbell, W.H., Field Determination of Nitrate using Nitrate Reductase, Field Analytical Methods for Hazardous Wastes and Toxic Chemicals. Air & Waste Management Association, 1997: pp. 851-860, Pittsburgh, PA)

Above information is courtesy of NECi (The Nitrate Elimination Company, Inc.)