Rapid forensic selected reaction monitoring liquid chromatography/mass spectrometry determination of ionophore antibiotics found at toxic levels in animal feeds.

A rapid, accurate, and selective method was developed for the forensic determination of ionophore antibiotics in animal feeds. A simple extraction procedure and liquid chromatography/tandem mass spectrometry (LC/MS/MS) in the selected reaction monitoring (SRM) mode were used for rapid identification and confirmation of monensin and lasalocid in feed samples and for quantitation of monensin. Extracts from a homogenous portion of ground feeds were prepared using liquid-solid extraction and liquid-liquid extraction techniques. Feed extracts were further purified by a simple defatting and solvent wash step and then concentrated to dryness. Feed extract residues were reconstituted in 1 mL LC mobile phase and a 2 microL aliquot injected into the SRM LC/MS system. The latter system used a C18, 100 x 2.0 mm, LC column coupled to a PE-Sciex API 2000 tandem triple quadrupole mass spectrometer equipped with a TurbolonSpray LC/MS interface. Feed samples were extracted and analyzed for the determination of monensin and lasalocid within a couple of hours. Control feed samples fortified with monensin at concentrations from 50 ppb to 5 ppm provided a linear response and calibration curve across this range with a correlation coefficient of 0.996.