Spectrophotometric Analysis of Primary Aliphatic Amines with Dichlone

Abstract

A spectrophotometric method is described for the determination of some primary aliphatic amines of pharmaceutical interest via reaction with dichlone (2,3-dichloro-l,4-naphthoquinone). A mixture of an ethanolic solution of the amine, or amine salt and sodium bicarbonate, with the chromogenic reagent was heated at 65° for 25 min. After acidification to pH 4, the majority of amines yielded an orange-colored product, λmax 475 nm. Some compounds reacted without heat, yielding other colors such as rose (500 nm. with piperazine), yellow (420 nm. with cysteine), and blue (630 nm. with isoniazid) suggesting different products. Molar absorptivities ranged from 900 to 5000. Under the described assay conditions, only primary aliphatic and cyclic secondary amines reacted. Primary aromatic (except some readily oxidizable ones), secondary or tertiary aliphatic, and/or aromatic amines were found not to interfere. The pharmaceutical compounds assayed included histamine, norepinephrine, serotonin, neomycin, leucine, cysteine, aminocaproic acid, ethanolamine, aminophylline, piperazine, and isoniazid. The amines are assayed in the 0.005-0.15-mg./ml. range with a relative standard deviation of 0.02-0.03. The possible composition of the colored products is discussed.