Differentiation of isomeric polyaromatic hydrocarbons by electrospray Ag(I) cationization mass spectrometry.

Abundant Ag(I)-cationized complexes of 13 polyaromatic hydrocarbons (PAHs), Ag+PAH and Ag+2(PAH), were readily generated by electrospray ionization (ESI). In-source collision-induced dissociation (CID) of the Ag+2(PAH) complex yielded the monomer complex Ag+PAH, which fragmented further to yield the radical molecular ion PAH. Based on significant differences in relative intensities of Ag+2(PAH), Ag+PAH and PAH, isomeric PAHs can be differentiated. The PAH/Ag+PAH ion intensity ratio was found to increase with decreasing ionization potentials (IPs) of PAHs. The ratio was significantly different for the isomeric PAHs studied over a wide range of PAH concentrations (1.6-100 nmol/mL), and showed good measurement reproducibility; the coefficient of variation of inter-day measurements was in the range 3-12% for four representative PAHs (n = 5). Detection limits for phenanthrene, pyrene, chrysene and benzo[a]pyrene, in the form of the monomer complexes (107)Ag+PAH and measured in the selected-ion monitoring (SIM) mode, were 0.31, 0.63, 0.16 and 1.25 pmol/5 microl injection, respectively (S/N ratio approximately 2-3).