Speciation of As(III) and As(V) in water samples by dispersive liquid-liquid microextraction separation and determination by graphite furnace atomic absorption spectrometry

A new method for the determination of inorganic arsenic species (As(III) and As(V)) was developed by dispersive liquid-liquid microextraction (DLLME) separation and graphite furnace atomic absorption spectrometry (GFAAS) detection. In the pH range of 3–5, As(III) complexes with ammonium pyrrolidinedithiocarbamate (APDC) and then can be extracted into carbon tetrachloride droplets formed by injecting the binary solution of carbon tetrachloride (extraction solvent) and methanol (dispersive solvent) into the sample solution. As(V) is not extracted at the same pH conditions and remained in the aqueous phase. After extraction and phase separation by centrifugation, the enriched As(III) in the sedimented phase was determined by GFAAS. Total inorganic arsenic was determined after reduction of As(V) to As(III) with sodium thiosulfate and potassium iodide, and As(V) was calculated by difference. Under optimized conditions, the detection limits of this method for As(III) were 36 ng L−1 with an enrichment factor of 45, and the relative standard deviation (R.S.D.%) was 3.1% (n = 11, c = 1.0 ng mL−1). The method has been applied to the speciation of As(III) and As(V) in natural water samples with satisfactory results.