Fast multi-residue screening for 84 pesticides in tea by gas chromatography with dual-tower auto-sampler, dual-column and dual detectors

A fast multi-residue screening method for determining pesticides in tea is described. Pesticides are extracted from tea with acetone and methylene chloride, then enriched and cleaned up with solid phase extraction (SPE) prior to gas chromatographic determination. The fast screening is achieved by a gas chromatograph system equipped with dual-column, dual-tower auto-sampler and both electron capture detector (ECD) and flame photometric detector (FPD). Optimal conditions are investigated for the prospective pesticides including column selection, detection mode, the retention behaviors, quantitative calibration, as well as the recoveries and repeatability of pesticides from tea samples. Under the optimal conditions, with the FPD-P detector accompanied CP-SIL 13CB column, 48 pesticides can be separated well and detected within 38 min; and with a DB-5 column, 35 ECD-detectable pesticides can be separated and detected within 46 min. The recoveries of 84 pesticides in tea samples are 65-120% with 0.34-16% RSD for spiking 0.02-3.0 mg/kg standard species. Because of the thermal instability of most pesticides, direct cold extraction of pesticides from a tea sample is recommended. The proposed method provided a very fast and efficient procedure to screen 84 pesticides from a complicated tea sample matrix