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

Tetracycline antibiotics, tetracycline, chlortetracycline, demeclocycline, doxycycline, minocycline, 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 +, Mg 2+, Ca 2+, Co 2+, Ni 2+, and Cu 2+ 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.