Blanking system for the spectrophotometric determination of ammonia in surface waters

Abstract

A reference stream is described for determining low levels (<0.5 mg l^–1 as nitrogen) of ammonia in surface waters using an automated phenate-hypochlorite procedure including a dual flow cell spectrophotometer. The only difference between the reference and colour-formation streams is the replacement of the nitroprusside catalyst by an equal flow of water. The calibration graph for the system was linear, and the mean standard deviation for duplicate analyses of routine samples was 0.0023 mg l^–1 as nitrogen for ammonia concentrations less than 0.080 mg l^–1 as nitrogen. The correlation between this spectrophotometric procedure and an automated distillation-spectrophotometric procedure exceeded 99.9%, with the results for the automated distillation-spectrophotometric procedure being an average of 1% higher.