Quantitation of quaternary ammonium compounds using electrospray mass spectrometry

A sensitive and specific electrospray mass spectroscopic assay has been developed for the quantitation of the series of quaternary ammonium surfactant compounds dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, and octadecyltrimethylammonium bromide and neostigmine bromide. Standard solutions were prepared in methanol, with an appropriate quaternary ammonium internal standard used in each case, and injected into a carrier solvent comprising acetonitrile (99%) and methanol (1%). Detection was based upon the positively charged quaternary ammonium ion in each case. Using this new technique, significant increases in sensitivity have been obtained over more traditional gas chromatographic-mass spectroscopic analytical techniques. All of the compounds tested were readily quantifiable at solution concentrations of 50 ppb, with linear correlations (r(2)>0.995) obtained over the range 50-300 ppb for the alkyltrimethylammonium bromides, and 50-200 ppb for neostigmine bromide. It is envisaged that, using this method, adsorption isotherms for these compounds on highly adsorbing activated carbons should be readily acquired. (C) 1998 Elsevier Science B.V. All rights reserved.