Development of Organic Gas Steam–Liquid Extraction (OGS–LE) Method for the Extraction of Chlorpyrifos and Diazinon From Aqueous Samples and Determination by GC–FID

In this study was proposed a new analytical technique for the extraction of two organophosphorus pesticides (OPPS) in water samples followed by gas chromatography−flame ionization detector (GC−FID) analysis. This technique, called organic gas steam−liquid extraction (OGS−LE), was performed by using a special home-made extraction cell that was designed to extraction without emulsification and with high extraction efficiency by a small amount of organic solvent. In this method, 2 mL extraction solvent (n-heptane) was added to the assigned column in the extraction cell inside the heating chamber. The organic solvent column was warmed up at 78°C. The aqueous sample solution (25 mL) was injected into the assigned column in the extraction cell by a syringe. Using N2 flotation into the organic solvent, the gas steam of the organic solvent was transferred to the aqueous column. N2 bubbles in the aqueous column moved upward from the bottom and interacted with the aqueous phase. The organic gas steam, along with N2 bubbles, after desolations in the aqueous sample and supersaturating, was collected on the surface of the aqueous sample. By using N2 flotation, the organic solvent was collected on the top of the solution without emulsification. The organic solvent was collected by means of a microsyringe. Then, 1 μL of the collected organic solvent was injected into the GC−FID for analysis. One variable at a time (OVAT) was applied to investigate the optimum conditions of all the variables. The variables of interest in the OGS−LE were selected as extraction solvent type and volume, ionic strength, the temperature of the heating chamber, extraction time, flow rate of the carrier gas and volume of the sample solution. Using optimized variables in the extraction process, for chlorpyrifos and diazinon, the detection limits, the precisions and the linearity of the method were found 41.6 and 21.9 ng mL–1, 1.8 and 7.1 (RSD, n = 3), 50–5000 μg mL–1 and 50–5000 μg mL–1, respectively.