Cryogenic grinding pre-treatment improves extraction efficiency of fluoroquinolones for HPLC-MS/MS determination in animal tissue

An efficiency extraction of fluoroquinolones in chicken muscle was achieved by pulverizing it in a freezer mill before treatment with NaOH (10mM)/MeCN (1:1). The improvement of cryogenic grinding in the extraction was demonstrated for the same piece (whole leg) of four chickens treated with enrofloxacin in equal doses. A confirmatory method based on high-performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS) was used to analyze the extracts. The chromatographic separation was achieved in 5min with a Synergi Fusion-RP 80A (50 x 2mm, 4 mu m) column filled with a hybrid polymer. The HPLC was coupled with a detector based in a quadrupole-linear ion trap Q-TRAP that allows a confirmatory detection according to the European legislation. The specificity of the method was assessed by testing a number of representative blank muscle samples (n = 10) to verify the absence of potential interfering compounds. The limits of detection and quantitation were 2 and 5ng g(-1) of quinolones in muscle samples, respectively. The chromatographic method was demonstrated to be linear for the range studied (5-500ng g(-1)) with the P value for lack-of-fit in the ANOVA table greater or equal to 0.10 (calibration coefficient 0.9998 and 0.9996 for ciprofloxacin and enrofloxacin, respectively). The mean intra-day relative standard deviation (RSD) (n = 6, c = 50ng g(-1)) was 6%; inter-day assay gave a RSD of 12%. The extraction and clean-up were carried out in one step with very satisfactory recovery data (between 65 and 101%).