Photometric determination of octadecylamine with methyl orange

The reaction of octadecylamine with Methyl Orange in water at pH 2.5-4.0 was studied. Linear relationships were revealed between the decrease in the absorbance of an aqueous solution of Methyl Orange and the concentration of octadecylamine. Optimal conditions of the reaction were found. It was demonstrated that 50- to 200-fold amounts of lower aliphatic and aromatic amines and salts of lower quaternary ammonium bases do not interfere with the determination. Procedures were developed for the photometric determination of 0.083-1.0 μg/mL and 0.74-10 μg/mL octadecylamine.