Using multi-walled carbon nanotubes (MWCNTs) as a novel sorbent and a new special anionic chromatographic column for pesticide residues, an ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method was developed for the simultaneous direct determination of glufosinate ammonium and its metabolites 3-methylphosphino-propionic acid and N-acetylglufosinate ammonium in milk. The samples were extracted with methanol, cleaned up using MWCNTs, and degreased by high-speed centrifugation at low temperature. The analytes were separated on an Anionic Polar Pesticide (2.1 mm × 100 mm, 5 μm) column using a mobile phase containing 0.9% formic acid solution (A) and 0.9% formic acid solution-acetonitrile (B). The instrument was operated in the negative ion scanning mode with multiple reaction monitoring. Glufosinate ammonium was quantified by an internal standard method, and its two metabolites by an external standard method. The calibration curves for glufosinate ammonium and its two metabolites were linear in the concentration range of 1–50, 2–50 and 2–50 μg/L with correlation coefficient (R²) greater than 0.99. For these compounds, the limits of detection were 2.5, 5.0 and 5.0 μg/kg, and the limits of quantification were 5.0, 10.0 and 10.0 μg/kg, respectively. The recoveries ranged from 79.35% to 101.80%, with relative standard deviation (RSD) between 1.15% and 8.63%. The proposed method is characterized by simple pretreatment, stable chromatographic conditions, low impurity interference, high sensitivity and good accuracy, and is suitable for the determination of glufosinate ammonium and its metabolite residues in milk.

The objective of this study was to establish a method for detecting the residue of dicamba in cow milk by high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The sample was extracted with 0.5% formic acid in acetonitrile, and the extract was purified by sodium chloride salting out, and separated on an Acquity UPLC BEH C₁₈ column (100 mm × 2.1 mm, 1.7 μm) by gradient elution using a mobile phase composed of acetonitrile and 0.01% formic acid aqueous solution. Identification and quantification were achieved using an electrospray ionization source in the negative ion mode with multiple reaction monitoring (MRM). Under optimized pretreatment and instrumental conditions, good linearity was observed in the concentration range of 5.0–250.0 μg/L with correlation coefficient (r) more than 0.999. The limit of detection (LOD) and limit of quantification (LOQ) of the proposed method were 5 and 10 μg/kg, respectively. The recoveries of dicamba at spiked concentration levels of 10, 20 and 200 µg/kg were 104.3%, 101.5% and 96.2% with relative standard deviations (n = 6) of 3.0%, 2.0% and 1.5%, respectively. This method is simple, accurate, repeatable, and suitable for the rapid detection of dicamba in milk.