A robust, credible, and practical multiresidue method based on liquid chromatography/tandem/mass spectrometry (LC/MS/MS) was developed for the simultaneous determination of 9 macrocyclic lactone drugs (abamectin B1a, doramectin, erythromycin, ivermectin B1a, josamycin, kitasamycin, roxithromycin, tilmicosin, and tylosin A) in bovine, porcine, chicken, and sheep muscles. The drugs were extracted with acetonitrile, and the extracts were defatted with n-hexane and further cleaned up on a C18 solid-phase extraction cartridge. LC/MS/MS data acquisition was achieved by using the multiple-reaction monitoring (MRM) mode, i.e., 2 transitions, to provide a high degree of sensitivity and repeatability. Matrix-matched standard calibration curves were used to achieve the best accuracy of the method by compensating for the matrix effect. The calibration graphs were linear (r >0.998) from 10 to 1000 ng/mL for erythromycin, josamycin, kitasamycin, roxithromycin, tilmicosin, and tylosin, and from 5 to 250 ng/mL for abamectin, doramectin, and ivermectin. The average recoveries of the 9 drugs were between 64.5 and 105, calculated by using matrix-matched calibration, with relative standard deviation values ranging from 1.6 to 14. The limits of detection were 0.1 g/kg for erythromycin, josamycin, roxithromycin, and tylosin; 0.2 g/kg for tilmicosin and kitasamycin; and 0.5 g/kg for abamectin, doramectin, and ivermectin. For confirmation, the MRM ratios for the 9 drug residues in the samples and the solvent were evaluated and found to be within the ratio criteria set by the guidelines of the European Union.

A high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/ MS) method was established for the determination of fifteen beta-agonists (clenbuterol, ractopamine, salbutamol, cimaterol, mabuterol, tulobuterol, bambuterol, mapenterol, cimbuterol, zilpaterol, formoterol, clorprenaline, terbutaline, penbutolol and brombuterol) in animal urine. Perchloric acid solution was used to acidify the sample and precipitate protein in the sample. The sample was purified and concentrated by an HLB mini-column. The separation of the beta-agonist was performed on an Agilent 1100 HPLC system with a Eclipse XDB-C18 column by using gradient elution with methanol and water (containing 0.1% (v/v) formic acid) as the mobile phases at a flow rate of 1 mL/min. Qualitative and quantitative analysis of the fifteen beta-agonists, which were ionized by electrospray ionization interface (ESI), were carried out in multiple reaction monitoring (MRM) mode with API 4000 tandem mass spectrometry. The calibration curves showed good linearity in the mass concentration range of 0.25 - 20 microg/L with the correlation coefficients r > or = 0.999 5. The recoveries of the fifteen beta-agonists ranged from 62.1% to 107% at the spiked levels of 0.25, 1.0 and 10 microg/L. The relative standard deviations (n = 10) were between 3.5% and 9.9%. The limits of quantification (S/N > 10) were 0.25 microg/L for all the analytes. This method is simple, rapid, sensitive and accurate.