Development of a method based on dispersive liquid–liquid microextraction followed by partial vaporization of the extract for ultra–preconcentration of some pesticide residues in fruit juices

Abstract

A new simple and efficient method has been developed for the ultra–preconcentration of multiclass pesticide residues including penconazole, chlorpyrifos, ametryn, clodinafop-propargyl, diniconazole, oxadiazon, and fenpropathrin from some fruit juice samples based on evaporation of the sedimented organic phase obtained from dispersive liquid–liquid microextraction. The enriched target analytes were analyzed by gas chromatography–flame ionization detection. In the microextraction procedure, a mixture of iso-propanol as a disperser and 1,2-dibromoethane as an extraction solvent is quickly injected into an aqueous phase containing the analytes and centrifuged. Afterward, the sedimented phase is transferred into a special shaped vaporization vessel and vaporized with nitrogen gas stream until remaining about 2 µL of it. Eventually, 1 µL of the remained sedimented phase is removed and analyzed by separation system. The optimum extraction and disperser solvents were found to be 1,2-dibromoethane and iso-propanol, respectively. In addition, the optimum pH range was 6-8, and nitrogen gas stream at a flow rate of 90 mL min−1 in a downward oriented vessel was applied. Eventually, the limits of detection and quantification were obtained in the ranges of 45-78 and 149-261 ng L−1, respectively. Relative standard deviations at the concentrations of 300, 500 and 1000 ng L−1 of each analyte were ranged between 2.2% and 5.8% for intra-day (n = 6) precision. Inter-day (n = 3) precision at a concentration of 500 ng L−1 of each analyte was obtained in the range of 4.9-7.1%. In addition, enrichment factors and extraction recoveries were ranged from 1382-2246 and 55-89%, respectively. Finally, the method was successfully utilized in analysis of the target pesticides in the selected juices.