Simultaneous Determination of Emamectin, its Metabolites, Milbemectin, Ivermectin and Abamectin in Tomato, Japanese Radish and Tea by LC/MS

Abstract

We developed a simple and rapid analytical method for determining the residues of emamectin benzoate, milbemectin, abamectin, ivermectin and emamectin metabolites in tomato, Japanese Radish and Japanese tea by liquid chromatography/mass spectrometer (LC/MS) with electrospray ionization (ESI). A sample extracted with acetone was simply cleaned up using only a Sep-Pak C18, and then directly measured by LC/MS (ESI). Several LC/MS measurement conditions were studied that included the mobile phase, solvent for sample solution, range of calibration and standard deviation of the measurement. Detecting target macrocyclic lactone chemicals with methanol as the mobile phase was more sensitive than acetonitrile, especially, milbemectin. The detection limits of these chemicals were 0.1 to 0.5 ng/ml (10 μl injection), and they were similar or more sensitive to the previous fluorescence detection method. For the measurement of these chemicals in tomato, Japanese radish and tea by LC/MS (ESI), ion suppression was always observed. To compensate for such an effect, we used a matrix-matched calibration. This compensation method is effective for obtaining accurate values. The recoveries by the developed method were in an acceptable range for the screening method and 90.1-120.9% except for milbemectin and abamectin from tea leaves that had interfering peaks.