Determination of Organophosphorus Pesticides in Groundwater by Gas Chromatography with Enrichment on Solid Phase Extraction Membrane

Solid phase extraction membrane, with polymer of phenyethylene/divinyl benzene as adsorbent was used to enrich organophosphorus pesticides (OPPs) in groundwater, and after desorption from the membrane, the desorption solution of acetone was used directly in GC analysis. For enrichment and separation of 6 OPPs, 500 mL of water sample were taken, 2.5 mL of CH₃OH were added, and the acidity of the sample solution was adjusted to pH 6.0 dropwise addition of φ 20% of HCl solution or 200 g·L^-1 of NaOH solution. The solution was then passed through the SDB-XC solid phase extraction membrane at a flow-rate of 100 mL·min^-1. The membrane was taken down, folded up and transferred into the 10 mL brown-glass bottle, 2.0 mL of acetone and about 0.2 g of Na₂SO₄ were added to the bottle which was then closed tightly with its ground stopper. The 6 OPPs adsorbed on the membrane were desorbed ultrasonically for 7 min at 30℃, and after keeping in dark for 5 min, an aliquot of 0.50 mL of the acetone solution was taken and amounts of the 6 OPPs were determined by GC with FPD. It was found that linear relationships between values of peak areas of the 6 pesticides and their mass concentrations in definite ranges were obtained, with their detection limits (3S/N) all less than 0.01 μg·L^-1. 7 portions of testing sample with addition of 0.10 μg·L^-1 of mixed standard solution of the 6 OPPs to blank water solutions as matrixes, were analyzed by the proposed method, and values of RSDs found were in the range of 4.3%-7.6%. Three water samples collected from various regional areas were taken as matrixs, and standard solutions of the 6 OPPs at 3 concentration levels (0.05, 0.10 and 0.70 μg·L^-1) were added to each of the 3 samples, and recovery were tested by the proposed method, values of recovery found for each of the 6 OPPs were greater than 76.0%.