Gas chromatography-mass spectrometric determination of ivermectin following trimethylsilylation with application to residue analysis in biological meat tissue samples

Abstract

A gas chromatography-mass spectrometric (GC-MS) method utilizing electron impact ionization has been developed for the quantitation of the antiparasitic agent, ivermectin (IVM). The approach is based upon the pre-column derivatization of IVM by reaction with N,O-bis(trimethylsilyl)tri-fluoroacetamide (BSTFA) in the presence of 1-methylimidazole as catalyst and carbon tetrachloride as solvent to form the trimethylsilyl (TMS) derivative of IVM (IVM-TMS) prior to injection into the GC-MS system. The derivatization reaction is complete within 5.0 min at room temperature and allows the GC-MS determination of IVM. A limit of detection for IVM of 0.67 ng g⁻¹ was achieved (via monitoring the peak with m/z = 185 in the selective ion mode and benzophenone-d₁₀ as the internal standard). The method was utilized with success for the determination of IVM in spiked horse meat samples yielding recoveries very similar to that obtained using a reference liquid chromatography-mass spectrometric method (LC-MS). In addition, this GC-MS method can be employed to determine not only IVM but also other related macrolide veterinary drugs such as eprinomectin and moxidectin which are often administered along with IVM. Detection limits of 3.72 and 5.44 ng g⁻¹ were obtained for eprinomectin and moxidectin, respectively.