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 ionization mass spectrometry and tandem mass spectrometry (MS/MS) methods for the determination and quantification of four quinolone antibiotics were adapted from a published procedure for liquid-liquid extraction from catfish muscle and high-performance liquid chromatographic analysis. In-source collision-induced dissociation was used to optimize fragmentation to produce mass spectra consisting of the protonated molecule and two characteristic fragment ions of nearly equal intensity. Selected ion monitoring of three ions per quinolone yielded sensitive detection 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 (< or equal to 10% deviation) between ratios derived from fortified catfish extracts and those from standard quinolones. MS/MS was used to increase 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 monitoring of the [MH - 18]+ transition for each quinolone yielded the highest sensitivity analysis in catfish extracts (estimated instrumental detection limits 0.08-0.16 ppb).