Monitoring quinolone antibacterial residues in bovine tissues: extraction with hot water and liquid chromatography coupled to a single- or triple-quadrupole mass spectrometer

A rapid and sensitive procedure for determining residues of seven quinolone antibacterials in bovine muscle, kidney and liver is presented. The method is based on the matrix solid-phase dispersion (MSPD) technique with hot water as extractant followed by liquid chromatography/single quadrupole mass spectrometry (LC/MS) or triple-quadrupole mass spectrometry (LOMS/MS). After dispersing tissue samples on hydrazine sulfate treated sand, target compounds were eluted from the MSPD column by passing through it 4mL of water heated at 100 degrees C. After pH adjustment and filtration, 200 and 5 mu L of the aqueous extracts were respectively injected into the LC/MS and LC/MS/ MS instruments. With the former instrument, NIS data were acquired in the three-ion selected ion monitoring mode, while MS/MS data acquisition was performed in the multi-reaction monitoring mode by selecting two precursor ion to product ion transitions for each target compound. Hot water appeared to be an efficient extracting medium, since absolute recoveries of the analytes were 84-102%. Using norfloxacin (a quinolone not used in veterinary medicine) as surrogate internal standard, the accuracy of the method at three concentration levels equal to 0.5, 1 and 1.5 times the maximum residue limits (MRLs) set by the european union was 88-109% with relative standard deviations (RSDs) not higher than 7%. The use of LC/MS/MS allowed detection and quantification of the analytes in any tissue considered to be performed at concentrations by far lower than half of their MRLs. Vice versa, the single-quadrupole NIS arrangement, while succeeding in monitoring quinolones in muscle tissue at the 0.5 MRL level, showed to be not sufficiently selective for unambiguous identification of some quinolones in kidney and liver.