QuEChERS Sample Preparation for LC–MS-MS Determination of Avermectins in Meat and Milk

Introduction

Avermectins are sixteen-membered ring macrolide drugs that are used as veterinary antihelmintics. The lowest allowable limit for these compoundsin food products is set based on worldwide safety evaluations. Regulatory MRLs for avermectins can vary worldwide but are generally in the ppb concentrationrange. The sensitive analysis of avermectins in food products such as milk and meat can be challenging due to their complex sample matrices.

QuEChERS is a simple and straightforward sample preparation technique that involves a salting-out liquid extraction followed by optionaldispersive solid-phase extraction (dSPE). Sample preparation using QuEChERS allows for fast throughput and high sensitivity analysis of food products.Although QuEChERS is commonly used for multiresidue pesticide analysis in fruits and vegetables, it is also applicable in the analysis of veterinary drugs inlivestock products. In this application note, milk and ground beef are prepared and analysed for avermectins at the ppb level, using QuEChERS methodology andLC–MS–MS.

Instrumentation & Consumables

Sample Preparation

Initial Extraction (QuEChERS)

Whole milk or ground beef was placed into a 50 mL centrifuge tube. 10 mL acetonitrile was added and the tube was shaken vigorously for 1 min. Thecontents of DisQuE pouch salts for CEN QuEChERS (p/n 186006813) was added and the tube was shaken again for 1 min. The sample was centrifuged and a 1 mLaliquot of the supernatant was taken for dSPE cleanup.

dSPE Cleanup

A 1 mL aliquot of supernatant was transferred to a 2 mL dSPE cleanup tube containing magnesium sulphate and C₁₈ sorbentand shaken vigorously for 1 min. The sample was centrifuged and an aliquot was transferred to a Maximum Recovery Vial (p/n 600000670 CV) forLC–MS–MS analysis.

UPLC Conditions

System: ACQUITY UPLC

Column: XSelect CSH C18 XP Column, 130 Å, 2.5 µm, 2.1 mm × 100 mm (p/n 186006103)

MS Conditions

System: Xevo TQ-S

Ionization mode: Electrospray positive (ESI⁺ )

Results & Discussion

For the analysis of avermectins in challenging matrices like whole milk and ground beef, good recoveries were obtained using DisQuE pouch samplepreparation. The incorporation of a dSPE clean-up step prior to LC–MS–MS analysis aids in the reliable quantitation of avermectins at low ppbconcentrations in complex matrices.

Conclusion

The DisQuE pouch (QuEChERS) protocol is an easy and effective method for the extraction of avermectins from livestock products. DisQuE samplepreparation provides excellent sample and minimal matrix effects. DisQuE extraction combined with LC–MS–MS analysis using eXtendedPerformance [XP] 2.5 µm columns provides low ppb quantitation of avermectins in complex matrices, enabling reliable testing.

For complete experimental details, go to www.waters.com/720004440

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