Two-step separation and determination of inorganic As species in water, soil and sediment samples by implementing two ionic liquids in dispersive liquid–liquid microextraction with electrothermal atomic absorption spectrometry detection

Abstract

A highly efficient liquid-liquid microextraction method based on two magnetic ionic liquids (MILs) as extraction solvents for the determination of inorganic As species in water, soil and sediment samples, with electrothermal atomic absorption spectrometry detection, was developed. First, As(III) species was separated by chelation with ammonium pyrrolidine dithiocarbamate and then extracted by the MIL trihexyl(tetradecyl)phosphonium hexachlorodisprosiate ([P6,6,6,14]3DyCl6). The As(V) species remaining in the aqueous phase was preconcentrated by extraction in the MIL trihexyl(tetradecyl)phosphonium tetrachloroferrate ([P6,6,6,14]FeCl4) at 2 mol L-1 HCl. The MIL phase containing As(V) was separated by a magnetic rod and diluted in chloroform. Then, an aliquot was injected into the graphite furnace for As determination. Total inorganic As was determined using the MIL [P6,6,6,14]FeCl4 as the extraction solvent at 0.5 mol L-1 HCl to achieve the same extraction efficiency for both species. The concentration of As(III) was calculated by the difference between total inorganic As and As(V) concentration. An extraction efficiency of 99% for As(V) and an enhancement factor of 35 were obtained with 5 mL of sample. The method detection limits were 17 ng L-1, 0.11 ng g−1 and 0.13 ng g−1 for As(V) and 20 ng L-1, 0.13 ng g−1 and 0.14 ng g−1 for As(III) in water, soil and sediment samples, respectively. The relative standard deviations for six replicate measurements of 3 µg L-1 for As(V) and As(III) were 3.1% and 3.9% respectively. The calibration linear range was 0.05?13 µg L-1. The method was successfully applied for inorganic As species determination in water, soil and sediment samples.