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Medientyp: E-Artikel Titel: Formation of gas‐phase clusters monitored during electrospray mass spectrometry: a study of quaternary ammonium pesticides Beteiligte: Evans, Catherine S.; Startin, James R.; Goodall, David M.; Keely, Brendan J. Erschienen: Wiley, 2001 Erschienen in: Rapid Communications in Mass Spectrometry, 15 (2001) 15, Seite 1341-1345 Sprache: Englisch DOI: 10.1002/rcm.378 ISSN: 0951-4198; 1097-0231 Schlagwörter: Organic Chemistry ; Spectroscopy ; Analytical Chemistry Entstehung: Anmerkungen: Beschreibung: AbstractGas‐phase cluster formation between the quaternary ammonium pesticides paraquat, diquat, difenzoquat, chlormequat and mepiquat, and chloride and acetate anions present in a liquid chromatography (LC) mobile phase, has been studied using electrospray mass spectrometry. The clusters of paraquat, mepiquat and chlormequat were revealed over the entire m/z range of the mass spectrometer, and their formation is dependent on the concentrations of both the cationic and the anionic species. Mepiquat and chlormequat form clusters of the type [2Mq+ + A−]+, where Mq+ is the quaternary ammonium cation and A− is the anion. Paraquat forms a cluster species with ammonia and also an ion‐pair complex with chloride anions. Diquat and difenzoquat did not form observable ion‐pair complexes or clusters with any of the anions studied. Competitive binding of acetate and chloride anions reflects the higher charge density of chloride, which forms the dominant clusters with mepiquat and chlormequat. The formation of cluster species has implications for the quantification of quaternary ammonium pesticides and may have an influence on the linearity of calibrations. Copyright © 2001 John Wiley & Sons, Ltd.