The INQUEST NITRATE SCREEN kit is a colorimetric test for the measurement of nitrate in surface water, groundwater and drinking water.  The nitrate screen is based on the reduction of nitrate to nitrite by zinc, followed by the formation of an azo dye.  Color developed is proportional to the concentration of nitrate and nitrite in the sample.  Test results are interpreted by visual comparison to a color chart, or by spectrometric determination at 550 nm using a photometer .