GC Determination of Resedues of 5 Organic Phosphorus Pesticides in Cauliflower with Dual-Column-Dual-Sample-Introduction

A portion (25 g) of the smashed and pretreated sample was extracted ultrasonically with 50 mL of acetonitrile for 10 min and filtered. The filtrate was shaked with 5 g of NaCl and stayed for phase separation. The acetonitrile phase 20 mL was taken and evaporated to near dryness by N₂-blowing in a water-bath at 70 ℃. The residue was taken up and made up to 5.0 mL with acetone for GC analysis. An aliquot of 5 μL was introduced into GC-column 1 (DB-17 capillary column, with pulse-nonsplitting sample introduction) for separation and preliminary screening. In happening of positive sample, another aliquot (1 μL) of the acetone solution should be taken for proof by separation on GC-column 2 (HP-5 capillary column, with non-splitting sample introduction). FPD⁺ detector and quantification by external standard method were used in both cases. Linearity ranges were found same between 0.02-0.20 mg·L^-1 for ethoprophos, phorate, phorate-sulfone, phorate-sulfoxide and triazophos for both columns. Detection limits (3S/N) were 1.0-3.0 μg·kg^-1 for GC-column 1 and 1.5-2.0 μg·kg^-1 for GC-column 2. Values of recovery found by standard addition method ranged from 79.6% to 119% and from 76.2% to 116%, and RSDs (n=10) were 2.8%-8.8% and 2.7%-8.4% for the 2 columns respectively.