An optimal manual procedure for ammonia analysis in natural waters by the indophenol blue method

Several procedures for ammonia determination in natural waters by the colorimetric indophenol blue method were tested. Solórzano's procedure, with phenol-alcohol, nitroprusside, alkaline citrate and hypochlorite as reagents, was shown to be appropriate for routine work. An improvement of this procedure was obtained by replacing hypochlorite with sodium dichloro-iso-cyanurate, by adding the catalyst after all other reagents, and by increasing the working pH. Concentration factors are statistically the same as in the original procedure, but the reagent blanks are lower and the color develops faster, both in fresh and in sea water.