MULTIRESIDUE DETERMINATION OF QUINOLONE ANTIBIOTICS USING LIQUID-CHROMATOGRAPHY COUPLED TO ATMOSPHERIC-PRESSURE CHEMICAL-IONIZATION MASS-SPECTROMETRY AND TANDEM MASS-SPECTROMETRY

Liquid chromatography coupled to atmospheric-pressure chemical ionizat ion mass spectrometry and tandem mass spectrometry (MS/MS) methods for the determination and quantification of four quinolone antibiotics we re adapted from a published procedure for liquid-liquid extraction fro m catfish muscle and high-performance liquid chromatographic analysis. In-source collision-induced dissociation was used to optimize fragmen tation to produce mass spectra consisting of the protonated molecule a nd two characteristic fragment ions of nearly equal intensity. Selecte d ion monitoring of three ions per quinolone yielded sensitive detecti on in catfish muscle extracts (estimated instrumental detection limits 0.8-1.7 ppb). The intensity ratios were used to confirm the presence of three of the quinolones based on the accurate agreement (less than or equal to 10% deviation) between ratios derived from fortified catfi sh extracts and those from standard quinolones. MS/MS was used to incr ease the specificity and sensitivity of analysis. Scans using constant neural loss (CNL) of 18 mass units gave a sensitive response for the quinolones suggesting that CNL scans may be applicable to multiresidue screening for unknown quinolones. MS/MS with multiple reaction monito ring of the [MH-18](+) transition for each quinolone yielded the highe st sensitivity analysis in catfish extracts (estimated instrumental de tection limits 0.08-0.16 ppb).