Development of a modified QuEChERS method for the determination of veterinary antibiotics in swine manure by liquid chromatography tandem mass spectrometry

• A modified QuEChERS approach was developed for determination of 26 veterinary drugs in the manure, and it is the first time that Pleuromutilins were included in such study.
• Different extraction solvents were investigated and modifications to accommodate a variety of target analytes.
• It provided a more convenient operation with improved recoveries compared to previous conventional SPE cleanup.
• The method is very economical and eco-friendly, especially in the environmental analyse with a large number of samples.

A QuEChERS (quick, easy, cheap, effective, rugged and safe) based methodology was developed for the rapid, simultaneous quantification and identification of 26 veterinary drugs in swine manure by liquid chromatography tandem mass spectrometry. The selected antibiotics included tetracyclines, sulfonamides, macrolides, fluoroquinolones, lincosamides and pleuromutilins. This is the first study to determine pleuromutilin levels in manure. The QuEChERS process involved two simple steps. First, sample extraction with methanol: acetonitrile: 0.1 M EDTA-McIlvaine buffer followed by phase separation with MgSO4: NaCl addition. The supernatant was then extracted and cleaned by dispersive solid-phase extraction using a primary-secondary amine (PSA) and octadecylsilane (C18) support. The proposed method provides a linearity in the range of 1–500 ng mL-1 and linear regression coefficients (r) were greater than 0.996. MDL and MQL ranged between 0.01–1.86 μg kg−1 and 0.05–5.91 μg kg−1, respectively. Recoveries ranged from 61.39 to 105.65% with the exception of sulfaquinoxaline (55.7–56.8%) and valnemulin (33.7–37.7%). This method resulted in good precision (repeatability and reproducibility) and relative standard deviations less than 17% within the same day, and lower than 20% between days. The method was then applied to study the swine manure samples collected from Guangdong, China. Chlortetracycline, tetracycline, doxycycline, sulfadimidine and tilmicosin were detected in all samples indicating high residuals in manure. In fact tilmicosin was detected at 14400 μg kg−1 suggesting that prudent treatment of manure should be conducted to prevent environmental contamination. In conclusion, this workflow can provide a simpler and more cost-effective alternative to conventional methods and is compatible with processing large sample numbers over a short time period.