A homogenous liquid–liquid extraction based on an acid–base reaction for extraction and preconcentration of some pesticide residues from aqueous samples

A simple, sensitive, and rapid sample pretreatment technique based on homogenous liquid–liquid extraction followed by gas chromatography–flame ionization detection has been developed for the extraction, preconcentration and determination of four pesticides including diazinon, oxadiazon, bromopropylate, and fenazaquin from fruit juice and vegetable samples. In this method, two parallel glass tubes with different diameters are connected with a teflon stopcock and used as an extraction device. Initially a basic organic solvent (amine) as an extraction solvent is mixed with acidified deionized water spiked with the analytes, which leads to formation of a homogenous solution. It is filled into one side of the extraction device. The other side is filled with an ammonia solution (1.9 M). Then the stopcock is opened and the solution of ammonia mixes with the aqueous phase. By this action, an acid–base reaction happens, so the homogenous solution is broken and the target analytes are extracted into the fine droplets of the organic solvent and move up through the aqueous phase which collect on the surface of the aqueous phase as a separated layer due to lower density of amine with respect to water. Then, 1 μL of the organic phase was taken and injected into the separation system for analysis. Under the optimum extraction conditions, high enrichment factors (1400–2125) and good extraction recoveries (56–85%) were obtained. The repeatability expressed as relative standard deviation, were in the ranges of 4.1–6.2 % (n = 6, C= 20 μg L–1) and 5.1–6.5% (n = 4, C= 20 μg L–1) for intra–day and inter–day precisions, respectively. Also, the method showed low limits of detection within the ranges of 0.04–0.32 μg L–1. Good repeatability, short sample preparation time and high enrichment factor are main advantages of the method.

A homogenous liquid–liquid extraction based on an acid–base reaction for extraction and preconcentration of some pesticide residues from aqueous samples Keywords:

homogenous liquid , liquid extraction , Gas chromatography , Pesticides , Fruit juices , Vegetables