Themethod requires only a spectrophotometer,
and is simple and cost-effective; sample preparation is rapid and a salt error or an interference by dissolved
organic carbon is not evident. Interferences induced by naturally coloured samples, or hydrogen sulphide can be
corrected or eliminated. A procedure for direct nitrate determination is given as well as a procedure to compensate
for the small loss of nitrite by nitric oxide formation for the nitrite present prior to the addition of a reductant