Promoted reaction microextraction for determining pesticide residues in environmental water samples using gas chromatography-mass spectrometry.

A microextraction technique termed promoted reaction microextraction (PRME) based on a liquid-liquid microextraction was developed by applying a chemical reaction for promoting the extraction of the analytes into the extracting solvent. PRME is a very simple, rapid and high-performance method for extraction and pre-concentration of organic compounds from water samples. In PRME, different types of chemical reactions can be used. In the present work, an acid-base reaction that produces a gaseous product is employed. In this method, appropriate amounts of auxiliary solvent (methanol), acidic promotor (oxalic acid), and extraction solvent (chloroform) were added rapidly into a water sample containing a basic promotor (sodium bicarbonate). After adding the solution containing the acidic promoter to the water sample containing the basic promoter, the acid-base reaction started with high intensity. The reaction product consisted of salt, water, and carbon dioxide gas. The produced carbon dioxide generated bubbles in the reaction medium that promoted the extraction of the analytes into the extracting solvent. After centrifuging, the fine particles of the extraction solvent were sedimented in the bottom of the conical tube. The denes phase was analyzed by gas chromatography-mass spectrometry (GC/MS). Several parameters affecting the extraction of 17 target pesticides by PRME-GC/MS (i.e., a selection of extraction solvent, extraction solvent volume, selection of auxiliary solvent, basic promotor content, and acidic promotor content) were investigated. Under the optimum conditions, the calibration graph was linear in the range of 0.035-40.0 µgL-1 with the detection limit of 0.003-0.035 µgL-1 for pesticides. The relative standard deviations (RSDs) of the PRME-GC/MS method were in the ranges of 2.29-4.76% (n = 3 and c = 0.30 µgL-1).