The Exchange of Trideuteromethyl Groups when Using Methane as a Reagent Gas in Chemical Ionisation Mass Spectrometry

Abstract

The use of isobutane (1) or ammonia (2) as reagent gases for quaternary amines has been reported. Work in our laboratories on the quantification of propantheline bromide (la) led to the development of a mass fragmentography assay using a trideutero- methyl analogue (lb) as the internal standard (3). Initial studies used methane as the reagent gas for chemical ionisation mass spectrometry (c.i.m.s.) and a displacement of the trideuteromethyl group by methyl was found to occur. A number of quaternary trideuteromethyl amines were prepared and examined using direct insertion c.i.m.s. and similar exchanges were found to occur for these (4). This paper reports our further investigation of this effect using gas chromatography mass spectrometry (gc-ms) and its extension to trideuteromethyl esters.