Determination of Avermectins in Sarda sheep wool by LC Orbitrap mass spectrometry

Wool is a fully sustainable renewable resource with low environmental impact. The technological characteristics make wools particularly suitable for different applications such as thermo-acoustic insulation, agricultural amendment, biomedical polymers, etc. Due to the accumulation and deposition of chemicals on fleece, sheep fleece represents a specific chemical indicator, and the concentration of the elements it contains reflects the feed and nutrition quality and the general health status as well as the climatic and environmental conditions. In addition, it has been shown that wool fibers are good bio-indicators of the environmental status (soil, water and air pollution). Furthermore, the presence of veterinary drug residues in raw wool is a major concern for human health and can have negative effects on the quality of wool based products. Among the most common veterinary drugs, avermectins are macrocyclic lactones, which have high anthelmintic, insecticide and acaricide activity. In order to understand whether the wool fibers can be vehicle of exposure to toxic substances both for humans and the environment, we developed a method to assess the presence of drug residues derived from veterinary practices. The aim of this work was to identify and quantify Avermectins in Sarda sheep wool by using High performance liquid chromatography coupled with Orbitrap mass spectrometry (LC-ESI-MS/MS). Microwave assisted extraction (MAE), an eco-friendly method, was optimized determining the best combination of type of solvent, solventamount, and duration of the extraction. Taking into account that wool is a complex matrix that contains fat, is rich in protein, and often interferes with the analytical procedures, SPE Oasis hydrophilic lipophilic balance (HLB) cartridges extraction method was selected as a cleanup step. Chromatographic separation was achieved on a Gemini C18 column using a linear gradient of methanol-ammonium formate 1 mmol containing 0.1% formic acid. The ionization was obtained in Electrospray (ESI) operating in positive ion mode. The mass spectrometer worked in tSIM-dd MS/MS mode with the fragmentation of precursor ions in the HCD cell. The complete MS acquisition was performed with resolving power FWHM 70000 and 17500 for the parent ions to fragment ions with a mass accuracy of 5 ppm. The validated method was finally applied to the analysis of real wool samples obtained from sheep of different areas of Sardinia.