Analysis of a residual diamine in a pharmaceutical polymer using solid phase extraction with analysis by gas chromatography mass spectrometry

Abstract

A method was developed for the analysis of 4,4′-methylenebiscyclohexylamine (DMDA) and 4,4′-methylenedicyclohexylisocyanate (DMDI) in a pharmaceutical polymer. The DMDA was extracted from the polymer with either buffer (0.1 M potassium phosphate pH 3.1) and the extract was passed through a SCX solid phase extraction cartridge. It was eluted from the cartridge with methanolic ammonia and then converted to its heptafluorobutyramide (HFB) derivative prior to analysis by gas chromatography–negative chemical ionisation mass spectrometry (GC–MS) in the negative ion chemical ionisation (NICI) mode. It was not possible to directly measure DMDI and it was thus analysed by selecting extraction conditions such that it would decompose to DMDA. The quantification of the residues in the polymer was based on the method of standard additions since this gave a better indication of the recovery from the complex matrix.