Solvent-Impregnated Agarose Gel Liquid Phase Microextraction for the Analysis of Triazine Herbicides in Water

Abstract

A new microextraction procedure termed agarose gel liquid phase microextraction (AG-LPME) was developed. The method uses an agarose gel disc that serves as holder for the acceptor phase. The solvent-impregnated agarose gel disc was prepared by slicing gelled agarose and exchanging the solvent from water to ethanol and then to 1-octanol that functioned as the extractant and impregnation solvent. The AG-LPME method was combined with gas chromatography-mass spectrometry (GC-MS) and applied to the determination of selected triazine herbicides as model compounds namely atrazine, secbumeton and cyanazine in wáter samples. The extraction procedure was performed by tumbling a solvent-impregnated agarose gel disc freely in the sample solution under optimized stirring rate and allowing the analytes to diffuse into the extraction solvent immobilized in the agarose gel disc. The interface was disrupted by centrifugation and 1-octanol was withdrawn for analysis. Each disc was discarded after single use, thus avoiding any analyte carry-over effect. The calibration results showed good linearity where the correlation coefficients (r) obtained were in the range of 0.9973 to 0.9992 for all triazines analyzed. The LODs were calculated based on the three times standard deviation of the noise and the results were in the range of 0.02 to 0.04 µg L^-1. Relative recovery studies were conducted by spiking drinking water and river water samples to give final concentrations of 5 and 80 µg L^-1. Results showed that excellent average relative recoveries in the range of 91.4 to 102.3% were obtained with low relative standard deviations (RSDs) of less than 7%. Experiments were carried out to compare the performance of AG-LPME and hollow fiber (HF)-LPME under their respective optimized conditions using deionized water samples adjusted to pH 4 and spiked with the analytes at 4 µg L^-1. It was found that extraction efficiency of AG-LPME is superior as compared to HF-LPME, except for atrazine. This new technique combines extraction and preconcentration approaches using an environmentally-compatible interface and microextraction mode that fulfils the green chemistry concept.