Identification of tetracycline antibiotics by electrospray ionization in a quadrupole ion trap

Tetracycline antibiotics, tetracycline, chlortetracycline, demeclocycline, doxycycline, minocy dine, methacycline, oxytetracycline, and anhydrotetracycline, are examined by electrospray ionization in a quadrupole ion trap. Studies were undertaken to evaluate the use of metal complexation as an alternative to conventional proton attachment. A variety of metal cationization processes, including attachment of Na+, Mg2+, Ca2+, Co2+, Ni2+, and Cu2+ were probed. Infrared multiphoton photodissociation and collisionally activated dissociation (CAD) were compared for generation of diagnostic fragmentation patterns of protonated and metal cationized tetracyclines. The photodissociation spectra provide a more informative signature, including more low mass ions that are not observed upon CAD. The metal complexes dissociate by pathways that are similar to those observed for the protonated molecules. (C) 1998 American Society for Mass Spectrometry.