Determination of multi-class antimicrobial residues in soil by liquid chromatography-tandem mass spectrometry
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: Na2EDTA–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 μg kg−1, with correlation coefficients higher than 0.99. The limits of detection and limits of quantification ranged from 0.01 to 2 μg kg−1 and 0.04 to 5 μg kg−1, 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 μg kg−1 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 μg kg−1 of chlortetracycline was detected in a soil sample. The results indicate that the proposed method has good feasibility.