New sorbents based on poly(methacrylic acid-TRIM) and poly(vinylimidazole-TRIM) for simultaneous preconcentration of herbicides in water samples with posterior determination by HPLC-DAD

Abstract

In the present study, new sorbents for solid-phase extraction (SPE) based on poly(methacrylic acid-trimethylolpropane trimethacrylate) (PMA-TRIM) and poly(vinylimidazole-TRIM) (PV-TRIM) for simultaneous extraction of tebuthiuron (TBT), hexazinone (HEX), diuron (DIU) and ametryn (AME) and posterior determination by HPLC-DAD were developed. The method was based on the preconcentration of 50.0 mL of water at pH 6.0 through 200 mg of each sorbent packed into a cartridge with further elution by 3.0 mL of methanol. The analytical curves were linear for the herbicides in the range 1.0–150.0 μg L⁻¹ with limits of detection (LOD) of 0.40, 0.31, 0.12, 0.34 μg L⁻¹ for TBT, HEX, DIU and AME, respectively, when using PMA-TRIM as the sorbent and 0.14, 0.44, 0.17 and 0.39 μg L⁻¹, respectively, when using PV-TRIM. The precision in terms of repeatability assessed as RSD (relative standard deviation, n = 10) for the multiresidue analysis ranged from 1.23% to 1.91% and 0.97% to 1.79% for respective concentrations of 10.0 and 100 μg L⁻¹ using the PV-TRIM polymer and 2.13% to 3.31% and 1.43% to 2.91% using PMA-TRIM. As observed, better analytical performance was achieved using PV-TRIM as the sorbent. The obtained analytical performance from the polymers, mainly PV-TRIM in terms of LOD and preconcentration factor (PF) was much higher compared to commercial sorbents octadecyl-C18-silica (C₁₈) and Amberlite® XAD4 poly(styrene-divinylbenzene) (DVB). Moreover, exceptional reusability was achieved (>161 recycles) without loss of adsorption capacity. To assess the accuracy of the preconcentration method, analyses of surface waters (well and river water), collected from an area near the cultivation of sugar cane, were carried out. From the recovery test ranging from 96% to 101%, it was concluded that the solid-phase extraction prior to HPLC-DAD analysis is appropriate and it is an alternative for multiresidue analysis in natural water.