Ionic liquid as ion-pairing reagent for liquid–liquid microextraction and preconcentration of arsenic species in natural waters followed by ETAAS

Abstract

A simple and highly efficient microextraction methodology was developed for arsenate [As(V)], arsenite [As(III)] and organic arsenic (i.e., DMA and MMA) preconcentration and determination based on the novel use of tetradecyl(trihexyl)phosphonium chloride ionic liquid (CYPHOS^® IL 101) as an ion-pairing reagent. As(V) species was selectively separated by forming As(V)-molybdate heteropoly acid [As(V)-MHPA] complex with molybdenum, followed by ion-pairing reaction with CYPHOS^® IL 101 and microextraction in chloroform. Arsenic detection was performed by electrothermal atomic absorption spectrometry (ETAAS). Under optimum conditions, the analyte extraction efficiency was 99% and yielded a preconcentration factor of 125 with only 5.00 mL of sample. The detection limit was 0.002 μg L⁻¹ as As(V). The relative standard deviation (RSD) for six replicate measurements at 1.5 μg L⁻¹ of As were 4.1%, 4.9% and 5.0% for As(V), As(III) and total organoarsenicals, respectively. The proposed methodology was successfully applied for As speciation analysis in several types of water samples.