Determination of 24 Pesticides including Pyrethroids, Organochlorines and Chlorothalonil in Underground Water by Gas Chromatography

High sensitivity is required to determine pyrethroids, organochlorines, chlorothalonil and chlorpyrifos by using Gas Chromatography-Micro-Electron Capture Detector (GC-μECD) due to their high electro-negativity. The sensitivity of pyrethroids, which have higher molecular weights, is much lower than organochlorines. Moreover, the efficiency of determination is very low by different analyses patterns. This problem has been solved by using a column pressure program, and 24 compounds were determined efficiently at the same time by optimizing column conditions and inlet temperature. The underground water sample was treated by liquid-liquid extraction, Florisil SPE cleanup and analyzed by RTX-CL Pesticides 2 with GC-μECD. The calibration curves for 24 compounds were linear in the range of 0.5-6000 ng/mL, and the method detection limits were in the range of 1.00-12.00 ng/L. The matrix spiked experiments were studied at three different concentration levels. The mean recoveries for low, middle and high concentration were in the range of 80.3%-116%, 79.9%-117% and 85.7%-102% with precisions of 1.5%-6.8%, 1.3%-7.6% and 1.1%-6.8%, respectively. Compared to common chromatographic column (DB-5MS), the special chromatographic column (RTX-CLPesticides 2) is more efficient for analyzing multiple targets and category compounds. The low sensitivity and peak tailing problem of pyrethroids caused by long residence time in column was solved by using a column pressure program. The method is sensitive, accurate, and economical and maintains a high flux, which is easy to determine multiple pesticide residues simultaneously.