Analysis of moxidectin by LC/MS and determination of residues in adipose and muscle tissues in commercial beef

Abstract

We have analyzed moxidectin residues in beef by a rapid and highly sensitive liquid chromatography-mass spectrometry (LC/MS) method without fluorescent derivatization. By using atmospheric pressure chemical ionization (APCI) with a fragment voltage of 100 V, good measurement results were obtained and the recoveries of moxidectin were 93.3% and 96.5% from adipose and muscle tissues, respectively. Identification of moxidectin residues in commercial beef was performed using three monitor ions. When quantitated at m/z 622, the levels of moxidectin were 35 ng/g in adipose tissue and 4.3 ng/g in muscle tissue. After adjustment for fat content and calculation of the moxidectin concentration on a fat basis, it was found that the moxidectin contents were the same in adipose and muscle tissues. Thus, it is considered that residual levels of moxidectin in adipose and muscle tissues are correlated to the fat contents in the tissues.