A NOTE OF CAUTION ON REDUCTION CONDITIONS WHEN USING THE CADMIUM COPPER COLUMN FOR NITRATE DETERMINATIONS IN AQUATIC ENVIRONMENTS OF VARYING SALINITIES

In a widely used method for nitrate determination in seawater, the reduction of nitrate occurs under acidic conditions because the sample is mixed with pure ammonium chloride. Under these conditions, about 40% of the nitrite formed is reduced further, leading to poor sensitivity and reproducibility. When the pH of ammonium chloride is adjusted to 8.5 with ammonia, the loss of nitrite is only about 5%, the sensitivity is improved by a factor of two, and the precision by a factor of five for seawater as well as freshwater. For samples of varying salinities ((0-30 ) S X 10(3)), the use of buffered ammonium chloride obviates the need for salinity corrections.