Simple assay for monitoring seven quinolone antibacterials in eggs: extraction with hot water and liquid chromatography coupled to tandem mass spectrometry. Laboratory validation in line with the European Union Commission Decision 657/2002/EC.

A simple and rapid method able to determine residues of seven quinolone antibacterials in whole eggs is presented here. This method is based on the matrix solid-phase dispersion technique with hot water as extractant followed by liquid chromatography-tandem mass spectrometry. After depositing 1.5 g of an egg sample containing the analytes and the analyte surrogate (norfloxacin) on sand (crystobalite), this material was packed into an extraction cell. Quinolones were extracted by flowing 6 mL of water acidified with 50 mmol/L formic acid through the cell heated at 100 degrees C. After pH adjustment and filtration of the extract, 100 microL of it was injected into the LC column. MS data acquisition was performed in the multiple reaction monitoring mode, selecting two precursor ion to product ion transitions for each target compound. Hot water appeared an efficient extracting medium, since absolute recoveries of the analyte in egg at the level of 20 ng/g were 89-103%. Estimated limits of quantification (S/N=10) were 0.2-0.6 ng/g. Based on the EU Commission Decision 2002/657/EC, the method was validated in terms of ruggedness, specificity, linearity, within-laboratory reproducibility, decision limit (CCalpha and detection capability (CCbeta). Depending on the particular analyte, CCalphas ranged between 0.41 and 2.6 ng/g, while CCbetas were 0.64-3.7 ng/g. The method was linear in the 3-30 ng/g range, with typical R(2) values higher than 0.97. The within-laboratory reproducibility (n=21) at 6 ng/g level was in the 9.0-12% range. After validation, a depletion study of enrofloxacin and one of its metabolites, i.e. ciprofloxacin, in eggs was conducted.