Analysis of protonated and alkali metal cationized aminoglycoside antibiotics by collision-activated dissociation and infrared multi-photon dissociation in the quadrupole ion trap.

Nine aminoglycoside antibiotics were analyzed in two quadrupole ion trap mass spectrometers using electrospray ionization. Structural information was obtained via collision-activated dissociation (CAD) and infrared multi-photon dissociation (IRMPD) of the protonated species. Several of the compounds, having multiple basic sites, preferred the doubly protonated form while some existed in the singly charged state or were distributed between single and doubly protonated species, allowing comparison of the fragmentation patterns of the two charge states. In general, IRMPD is as efficient as CAD, produces more low-mass fragment ions, and is more universally applied owing to its low dependence on trapping, pressure and tuning conditions. Alkali metal complexation using Li(+) and Na(+) was probed as a means of producing different fragmentation patterns, but in most cases the resulting fragmentation patterns were simplified versions of those obtained for the protonated analogs. Copyright 2000 John Wiley & Sons, Ltd.