Electrospray ionization and tandem ion trap mass spectrometry for the confirmation of seven beta-lactam antibiotics in bovine milk

The feasibility of a technique to confirm the presence of residues from sev en beta-lactam antibiotics in bovine milk has been demonstrated. The techni que makes use of electrospray ionization and tandem ion trap mass spectrome try, Residues are first extracted from milk by reversed-phase solid phase e xtraction. Target analytes are separated by on-line reversed-phase liquid c hromatography and ionized in the electrospray interface. The product ion ma ss spectra are acquired following collision-induced dissociation of protona ted molecules. Confirmation is based on comparison of full scan spectra bet ween unknowns and bona fide standards. The feasibility of this technique ha s been demonstrated for the six beta-lactams currently approved for use in lactating dairy cattle (penicillin G, ampicillin, amoxicillin, cloxacillin, cephapirin and ceftiofur) and a drug not approved for animal use, cefazoli n. The technique has been applied to control milk fortified at 5 ng/mL of p enicillin G and 10 ng/mL of the other six drugs. (C) 1998 John Wiley & Sons , Ltd.