Determination of Residue of Emamectin in Aquatic Products by Liquid Chromatography Tandem Mass Spectrometry

A method was proposed for the determination of residue of emamectin in aquatic products by liquid chromatography tandem mass spectrometry (LC-MS/MS). 5.00 g of aquatic product sample was taken and ultrasonically extracted for 10 min with 12.5 mL of ethyl acetate, and then shaken by oscillation for 15 min. The extraction was repeated once, and the combined supernatant was made its volume up to 25 mL with ethyl acetate. 0.5 mL of the above solution was taken and blown to dryness by nitrogen at 45℃, then the residue was dissolved in 1 mL of 80% (volume fraction) acetonitrile solution. After ultrasound, the above solution was purified by liquid-liquid extraction with 2 mL of acetonitrile saturated n-hexane solution. After purification, the lower layer solution was passed through 0.22 μm hydrophobic polytetrafluoroethylene (PTFE) filter membrane, and separated on Atlantis T3 column using a mixture of acetonitrile and 5 mmol·L^-1 acetic acid solution at different volume ratios for gradient elution, and determined by LC-MS/MS, with external standard method for quantitation. As shown by the results, linear relationship between the mass concentration of emamectin and the corresponding peak area was found in the range of 0.01-2.0 μg·L^-1, with the lower limit of determination (10S/N) of 0.5 μg·kg^-1. Test for recovery was made by the standard addition method, giving the results in the range of 84.3%-99.9%, with RSDs (n=6) of the determined values less than 7.0%. This method was applied to analysis of 50 actual samples, and emamectin was detected in only one imported salmon sample, with detection amount of 20.7 μg·kg^-1.