Quantitation of quaternary ammonium compounds using electrospray mass spectrometry

A sensitive and specific electrospray mass spectroscopic assay has been dev eloped for the quantitation of the series of quaternary ammonium surfactant compounds dodecyltrimethylammonium bromide, tetradecyltrimethylammonium br omide, hexadecyltrimethylammonium bromide, and octadecyltrimethylammonium b romide and neostigmine bromide. Standard solutions were prepared in methano l, with an appropriate quaternary ammonium internal standard used in each c ase, and injected into a carrier solvent comprising acetonitrile (99%) and methanol (1%). Detection was based upon the positively charged quaternary a mmonium ion in each case. Using this new technique, significant increases i n 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 corr elations (r(2)>0.995) obtained over the range 50-300 ppb for the alkyltrime thylammonium bromides, and 50-200 ppb for neostigmine bromide. It is envisa ged that, using this method, adsorption isotherms for these compounds on hi ghly adsorbing activated carbons should be readily acquired. (C) 1998 Elsev ier Science B.V. All rights reserved.