Speciation analysis of inorganic arsenic in water samples by immobilized nanometer titanium dioxide separation and graphite furnace atomic absorption spectrometric determination

A novel solid phase extraction sorbent, nanometer titanium dioxide immobilized on silica gel (immobilized nanometer TiO2), was prepared by sol–gel method, and the adsorptive potential of immobilized nanometer TiO2 for inorganic arsenic species (As(III) and As(V)) was assessed. It was found that both As (III) and As(V) could be adsorbed quantitatively on immobilized TiO2 within a pH range of 5.0–7.5, and only As(III) could be quantitatively retained on the sorbent within a pH range of 9.5–10.5 while As(V) was passed through the microcolumn without the retention. Based on this fact, a new speciation scheme for inorganic arsenic was established, which involved determining total As at pH 6.0 and As(III) at pH 10, with As(V) obtained by difference. The adsorption capacity of immobilized nanometer TiO2 for As(III) was found to be 4.22 mg g−1. Under the optimized conditions, the detection limits of this method for As(III) were 24 ng L−1 with an enrichment factor of 50, and the relative standard deviation (R.S.D.%) was 4.8% (n = 11, c = 5 ng mL−1). The proposed method has been applied to the speciation of inorganic arsenic in natural water samples with satisfactory results.