Development and validation of a solid phase extraction-UPLC-MS/MS method for the determination of fifty-nine antimicrobials in commercial organic fertilizers and amended soils

Abstract

Commercial organic fertilizers often contain high levels of antimicrobials that can be released into agricultural soils and pose potential ecological risks, and there is a significant need to quantify their occurrence in these products. However, the presence of high contents of organic matter, nutrient salts, and trace metals in commercial organic fertilizers pose significant challenges for the extraction and analysis of antimicrobials, especially when multiple compounds are targeted. This study developed a robust and sensitive multi-residue method for the determination of fifty-nine antimicrobials, belonging to four different classes, in commercial organic fertilizers and amended soils. The method was based on ultrasonic extraction with a mixture of EDTA-McIlvaine buffer/methanol/acetonitrile/acetone (5:2:2:1 by volume), solid phase extraction (SPE) using SAX and HLB cartridges in series, followed by UPLC–MS/MS analysis in the dynamic multiple reaction monitoring (MRM) mode. The performance of the optimized extraction method was good for fifty-nine antimicrobials with a median recovery rate of 46 and 84 % in commercial organic fertilizers and amended soils, respectively. The matrix effects were between 105 and 109 % in commercial organic fertilizers and 102–140 % in amended soils, which are indicative of the effectiveness of pretreatment procedures and the accuracy of instrumental analysis. The method had good linearity (R2 > 0.99), and the detection limits and method quantification limits for fifty-nine antimicrobials in commercial organic fertilizers were 0.002–0.206 ng/g (median 0.026 ng/g) and 0.006–0.684 ng/g (median 0.086 ng/g), respectively. This robust and practical method effectively eliminates the matrix effects of commercial organic fertilizer and could be used for routine determination of multiple classes of antimicrobial residues in commercial organic fertilizers and amended soils.