Residue analysis of tebufenozide and indoxacarb in chicken muscle, milk, egg and aquatic animal products using liquid chromatography-tandem mass spectrometry

We developed an analytical method using liquid-liquid extraction (LLE) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) to detect and quantify tebufenozide (TEB) and indoxacarb (IND) residues in animal and aquatic products (chicken muscle, milk, egg, eel, flatfish, and shrimp). The target compounds were extracted using 1% acetic acid (0.1% acetic acid for egg only) in acetonitrile and purified using n-hexane. The analytes were separated on a Gemini-NX C-18 column using (a) distilled water with 0.1% formic acid and 5 mm ammonium acetate and (b) methanol with 0.1% formic acid as the mobile phase. All six-point matrix-matched calibration curves showed good linearity with coefficients of determination (R-2) >= 0.9864 over a concentration range of 5-50 mu g/kg. Intra- and inter-day accuracy was expressed as the recovery rate at three spiking levels and ranged between 73.22 and 114.93% in all matrices, with a relative standard deviation (RSD, corresponding to precision) <= 13.87%. The limits of quantification (LOQ) of all target analytes ranged from 2 to 20 mu g/kg, which were substantially lower than the maximum residue limits (MRLs) specified by the regulatory agencies of different countries. All samples were collected from different markets in Seoul, Republic of Korea, and tested negative for tebufenozide and indoxacarb residues. These results show that the method developed is robust and may be a promising tool to detect trace levels of the target analytes in animal products.