Aliphatic Amine Interference in Indophenol Reaction for Ammonia-Nitrogen Determination and Its Possibility as Quantitative Method for Aliphatic Amines

Abstract

The indophenol reaction or the phenate method for ammonia-nitrogen determination described in standard analytical methods does not refer to aliphatic amine interference. However, the production of the blue color from a primary aliphatic amine was confirmed during the indophenol reaction by the procedure in Standard Methods of Analysis for Hygienic Chemist. Also, sodium nitroprusside used as a catalyst in the reaction was revealed to promote blue color formation. Formaldehyde and acetaldehyde were detected in color formation from methylamine and ethylamine, respectively; therefore, the production of ammonia and aldehyde via imine and/or iminium ions from a primary aliphatic amine was proposed as the mechanism of the color formation. Linear relationships between the concentrations of primary aliphatic amines and chitosan and their absorbances after the reaction indicated that the indophenol reaction using sodium nitroprusside would be an effective quantitative method for determining primary aliphatic amines and chitosan concentrations.