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A new analytical strategy based on liquid chromatography-tandem mass spectrometry (LC-MS/MS) combined with accurate mass high-resolution Orbitrap mass spectrometry (HR-Orbitrap MS) was performed for high-throughput screening, confirmation, and quantification of 22 banned or unauthorized veterinary drugs in feedstuffs according to Bulletin 235 of the Ministry of Agriculture, China. Feed samples were extracted with acidified acetonitrile, followed by cleanup using solid-phase extraction cartridge. The extracts were first screened by LC-MS/MS in a single selected reaction monitoring mode. The suspected positive samples were subjected to a specific pretreatment for confirmation and quantification of analyte of interest with LC-MS/MS and HR-Orbitrap MS. Mean recoveries for all target analytes (except for carbofuran and chlordimeform, which were about 35 and 45%, respectively) ranged from 52.2 to 90.4%, and the relative standard deviations were <15% except for 20% for carbofuran. The decision limits (CCαs) for target analytes in formulated feed were between 2.6 and 23 μg/kg, and the detection capabilities (CCβs) were between 4.2 and 34 μg/kg. The method was successfully applied to screening of real samples obtained from local feed markets and confirmation of the suspected target analytes. It provides a high-throughput, sensitive, and reliable screening, identification, and quantification of banned veterinary drugs in routine monitoring programs of feedstuffs.

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Antimicrobial residues in environmental matrices may result in the occurrence of antimicrobial-resistant bacteria in soil. In this paper, a new analytical method based on liquid chromatography-tandem mass spectrometry for multiresidue analysis of 24 antimicrobials of a wide polarity range and variable physicochemical properties, including sulfonamides, tetracyclines, fluoroquinolones, macrolides, lincosamides and pleuromutilins in soil was developed. Samples were extracted with an acetonitrile: Na 2 EDTA-McIlvaine buffer (pH 4.0, 5 : 5, v/v) system and then re-extracted with a 0.2 M sodium hydroxide solution. The extracts were purified using an HLB solid phase extraction cartridge.Chromatographic separation of the components was performed on a Zorbax SB-Aq column using acetonitrile-0.1% formic acid as mobile phase. The method developed was linear in a concentration range from the limits of quantification to 200 mg kg À1 , with correlation coefficients higher than 0.99. The limits of detection and limits of quantification ranged from 0.01 to 2 mg kg À1 and 0.04 to 5 mg kg À1 , respectively. The overall average recoveries for target analytes were more than 60% except for tetracycline (59.3%) in three spiked levels of 1, 4 and 20 mg kg À1 with relative standard deviations less than 20%. The method was further applied for the determination of residual antimicrobials in real samples. Some target antimicrobials were detected at different levels and tetracycline residues were dominant. 163.6 mg kg À1 of chlortetracycline was detected in a soil sample. The results indicate that the proposed method has good feasibility.

A sensitive and reproducible method based on high performance liquid chromatography with evaporation light scattering detection (ELSD) was developed for the simultaneous determination of 10 macrolides drugs such as azithromycin, tulathromycin, spiramycin, tilmicosin, tylosin, erythromycin, clarithromycin, roxithromycin, midecamycin and josamycin in feeds. Feed samples were extracted with a sodium borate buffer solution (pH 10.0) À ethyl acetate. The dry extracts were dissolved in a phosphate buffer solution (pH 8.0), and then applied to an Oasis HLB solid-phase extraction cartridge for cleanup. The residues were reconstituted in 0.5 mL of the mobile phase. By optimizing the main operational parameters of ELSD and chromatographic conditions, all target compounds were well separated on an Ecosil C 8 -SH column (250 mm  4.6 mm, 5 mm) using a gradient elution program. The calibration curves showed good linearity (r > 0.9985) in the range of 1-200 mg mL À1 for ten analytes. The average recoveries of all analytes from five kinds of feeds spiked at three levels were between 60.2% and 112%, with intra-day and inter-day relative standard deviations below 11% and 15%, respectively. The limits of detection ranged from 0.4 to 0.8 mg kg À1 for ten macrolides.