Synchronous detection of seven persistent pyrethroid pesticides in tea by MECC using reversed electrode polarity stacking concentration technique

For rapid detection of trace residues of pesticides in tea, a synchronous detection method for seven kinds of pyrethroid pesticide residues in sample was established with micellar electrokinetic capillary chromatography(CMECC) based on the on-column stacking. The optimal operation condition of on-column stacking was described as follows: the background solution consists of 15% isopropyl alcohol, 20% acetonitrile, 60 mmol/L sodium dodecyl sulfate (SDS) and 50 mmol/L tris (hydroxymethyl) aminomethane (Tris). After the extract of tea was cleaned by solid phase extraction for removing some impurities, and dried by nitrogen, the sample residue was dissolved in 1 mmol/L SDS solution. Reverse voltage was imposed after the 100s injection, and then the polarity was exchanged when the current returned to 95% of the normal. After on-column stacking, the enrichment factors of seven pyrethroid pesticide residues were higher than 17, and their recoveries were more than 82%. Under the optimal operation condition, the detected concentration limits of seven kinds of pyrethroid pesticide residues in tea were 0.05 mg/kg for cyhalothrin, 0.05 mg/kg for bifenthrin, 0.05 mg/kg for yfluthrin, 0.05 mg/kg for alpha-cypermethrin, 0.4 mg/kg for deltamethrin, 0.05 mg/kg for permethrin and 0.05 mg/kg for fenvalerate, respectively.