Electrospray and chemical ionization mass spectrometry of di-n-butyl sulfate. Unimolecular chemistry of its protonated form and quantification methodby liquid chromatography/electrospray ionization tandem mass spectrometry

Di-n-butyl sulfate (DNBS) has been studied by electrospray (EST) and chemic al (CI) ionization mass spectrometry. The use of methanol as solvent in ele ctrospray ionization allows observation of relatively abundant [DNBS + CH3O H + H](+) ions (m/z 243) which upon collision dissociate to [DNBS + H](+) i ons (m/z 211), In both ESI and CI experiments, it is found that [DNBS + H]( +) ions lead to m/z 113 daughter ions. The composition of this m/z 113 frag ment ion and its mechanism of formation have been established by high resol ution measurements and CID-MIKE experiments. An 'internal substitution' rea ction involving an ion-neutral intermediate is proposed to explain the form ation of a [C8H17](+) ion (m/z 113) by loss of a H2SO4 molecule. Finally, a LC/ESI-MS/MS quantification method is proposed in which a detection limit of di-n-butyl sulfate in the ppm range is obtained. It is suggested that th e quantification method might be extended to higher dialkyl sulfates. Copyr ight (C) 2000 John Wiley & Sons, Ltd.