Determination of Aliphatic Amines by High Performance Liquid Chromatography with Amperometric Detection after Derivatization with Phenylisothiocyanate

Abstract

Liquid chromatography with amperometric oxidative detection is proposed as a sensitive method for the determination of aliphatic amines previously converted in thioureido derivatives by reaction with phenylisothiocyanate (PIT). The phenylthioureas of four model amines, methylamine (MA), propylamine (PA), n-butylamine (BA) and isobutylamine (IBA) have been synthesized and isolated. Their electrochemical behavior on a glassy carbon electrode has been explored by cyclic voltammetry. The thioureido derivatives can be oxidized through two one-electron steps at acidic pH values, presumably involving the intermediacy of proton transfers. A mechanistic pathway is also proposed on the basis of experimental data. Liquid chromatographic parameters as mobile phase composition and flow rate, temperature and working electrode potential have been optimized. The method permits the simultaneous determination of the phenylthioureas of the selected amines with detection limits in the lower µgL–1 range.