| Abstract: | A simple and inexpensive liquid chromatography-tandem mass spectrometric method for the determination of anthelmintics in alfalfa plants (Medicago sativa L.) was developed and validated. Anthelmintics in plant leaves and stems (green chops) were extracted with methanol/acetonitrile (7:3, v/v) followed by a concentration and clean-up step using solid-phase extraction (Strata-X, 500?mg, 6?ml cartridge). After drying with nitrogen gas, the adsorbed analytes were eluted with methanol/acetonitrile (50:50, v/v) mixture followed by 100% acetonitrile. Chromatographic separation was achieved on an Atlantis T-3 (2.1?×?100?mm?×?3?µm) analytical column with a Phenomenex guard cartridge (C8, 4?×?3?mm) attached to a Waters triple quadrupole mass spectrometer operated in positive electrospray ionisation mode with selected reaction monitoring. Samples were analysed using gradient elution at a flow rate of 0.35?ml?min–1. The mobile phase consisted of a 10?mM ammonium formate solution in (A) water/acetonitrile (90:10, v/v) and (B) methanol/acetonitrile (50:50, v/v). The method was validated for levamisole, fenbendazole, fenbendazole sulphoxide and fenbendazole sulphone at 10, 20 and 40?µg?kg–1 and for eprinomectin at 20, 40 and 80?µg?kg–1. Limits of quantification (LOQ) were 10?µg?kg–1 for all analytes except eprinomectin, which had an LOQ of 20?µg?kg–1. The overall mean recovery in green plants was between 74.2% and 81.4% with repeatabilities ranging from 2.2% to 19.1% and reproducibilities in the range 3.8–8.7%. The validated method was applied to plant samples in a study on the behaviour of anthelmintic drugs in a soil, plant and water system. |
