Simultaneous identification and detection of four novel isoxazoline drugs in bovine-origin foods using ultra-high performance liquid chromatography coupled to quadrupole/linear ion trap mass spectrometry

Isoxazoline drugs （ISOs） are a class of five-membered heterocyclic compounds containing N and O atoms. They can inhibit <i>γ</i>-aminobutyric acid gated chloride channels and are widely used in the treatment of parasitic diseases in poultry. The intake of animal-derived foods by humans is an important way to come into contact with ISOs. Excessive use of ISOs can lead to their residues in animal-derived foods， thereby threatening human health and causing neurotoxicity and hepatotoxicity. To address the safety issues caused by ISO residues in animal-derived foods， an ultra-high performance liquid chromatography-quadrupole/linear ion trap mass spectrometry （UHPLC-Q/Trap MS） analytical method for four novel ISOs （fluralaner， sarolaner， afoxolaner， lotilaner） in bovine-origin foods （including milk， beef and bovine liver） was established. The sample was first extracted with acetonitrile and then purified with PRiME HLB solid phase extraction （SPE） column. Using 5 mmol/L ammonium acetate aqueous solution and acetonitrile as the mobile phase， after separation by Shim-pack GIST C18-AQ （100 mm×2.1 mm， 2.7 μm） chromatography column， the analysis was carried out in the multi-reaction monitoring （MRM） mode by information-dependent acquisition （IDA）， enhanced product ion scanning （EPI） and spectral library retrieval， and quantification was performed using the external standard method. The results showed that the four ISOs had good linear relationships within their respective mass concentration ranges. The correlation coefficients （<i>r</i>） were all ≥0.993 6， and the limits of detection （LODs） and quantification （LOQs） were 0.2-0.5 μg/kg and 0.5-1.0 μg/kg， respectively. Under the low， medium and high spiked levels （1， 2 and 10 μg/kg）， the recoveries of the four ISOs ranged from 67.6% to 118.9%， and the relative standard deviations （RSDs） ranged from 2.0% to 20.0%. In addition， in this study， qualitative screening and analysis of the target compounds were conducted through MRM-IDA-EPI combined with spectral library retrieval. Dual qualitative analysis of the target compounds was carried out based on information such as retention time and EPI fragment ions， which improved the accuracy of qualitative analysis and effectively eliminated the interference of false positive results. This method features low LODs and good recoveries. It is also simple and rapid to operate， with high sensitivity and accuracy. It can achieve qualitative and quantitative analysis of new ISOs residues in bovine-origin foods. This study can provide technical support for food safety agencies to implement preventive measures against new ISOs in animal foods.