A modified spectrophotometric method for the determination of ammonia (and amino-acids) in natural waters, with particular reference to sea water

Abstract

Strickland and Parsons have described a method for determining ammonia (and amino-acids) in sea water. This method, in which ammonia is first oxidised to nitrite with sodium hypochlorite, was found to be very time consuming and often imprecise. The results of a critical examination of the underlying chemistry have led to a modified procedure in which the time required for analysis has been reduced from 3·5 hours to 17 minutes. The modified procedure gave a coefficient of variation of 1·6 per cent. from the analysis of thirteen replicate aliquots of a sample of sea water containing approximately 20 µg 1^–1 of ammonium-nitrogen, and hence is suitable for determining ammonia concentrations in the order of 0 to 200 µg 1^–1. The response for 1 µg 1^–1 of ammonium-nitrogen, in either sea water or de-ionised water, was equivalent to an optical density change of 1·6 × 10^–3 per cm of solution. The procedure is also suitable for the quantitative determination of ammonia (and amino-acids) in other natural waters.