Detection of cationic surfactants in oral rinses and a disinfectant formulation using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Three commercial oral rinses and one commercial disinfectant formulation were analyzed for the presence of cationic surfactants using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) in the positive ion mode. The product labels on these formulations indicate the presence of cetylpyridinium chloride, tetraalkylammonium or trialkylbenzylammonium chlorides. The resulting MALDI-TOF mass spectra only showed cetylpyridinium, tetraalkylammonium, and trialkylbenzylammonium ions, apparently due to the dissociation of the salts in the ion source. We confirmed the presence of cetylpyridinium salt in the three oral formulations, whereas the disinfectant formulation consisted of a complex mixture of the salts of dioctyldimethyl-ammonium, didecyldimethylammonium, benzylmyristyldimethylammonium, decyloctyldimethylammonium, benzyldecyldimethylammonium, and benzylcetyldimethylammonium. This work demonstrates again the potential for using meso-tetrakis (pentafluorophenyl)porphyrin as a matrix in the MALDI-TOFMS analysis of low molecular weight compounds. This study also demonstrates that the mode of ionization of quaternary ammonium compounds (cationic surfactant salts) under MALDI conditions is by dissociation, leading to the detection of only the positively charged moieties. Copyright (C) 2001 John Wiley & Sons, Ltd.