Multi-residue analysis of veterinary drugs, pesticides and mycotoxins in dairy products by liquid chromatography–tandem mass spectrometry using low-temperature cleanup and solid phase extraction

• A multi-residue assay of veterinary drugs, pesticides and mycotoxins was developed.
• The method was demonstrated applicability in milk, yogurt, milk powder and cheese.
• We firstly applied low-temperature cleanup followed by SPE to purify dairy products.
• The temperatures and frozen time of the low-temperature cleanup were tested.
• The method was validated for each type of matrix, showing satisfactory parameters.

A multi-class multi-residue analysis method for determination of veterinary drugs, pesticides and mycotoxins in dairy products by liquid chromatography–tandem mass spectrometry (LC–MS/MS) has been established. These 17 classes, a total of 40 kinds of target compounds were chosen because their administration to food-producing animals is banned or regulated in China and may be potentially abused or misused. Samples were extracted with acetonitrile–ethyl acetate–acetic acid (49.5 + 49.5 + 1, v/v/v). Most of lipids in the extract were removed by low-temperature cleanup, prior to solid phase extraction on HLB cartridges. The quantification and confirmation of the 40 analytes were performed by LC–MS/MS with electro-spray ionization (ESI) interface in multiple reaction monitoring (MRM) mode. The limits of detection (LODs) and limits of quantification (LOQs) were 0.006–0.3 μg/kg and 0.02–1.0 μg/kg, respectively. The spiked recoveries in milk, yogurt, milk powder and cheese samples were from 67.3% to 106.9%. The repeatability and the within-laboratory reproducibility were less than 12.7% and 13.9%. Applying this method, our results revealed the presences of chloramphenicol, cimeterol, and flunixin at the concentration of 0.027–0.452 μg/kg in some samples.