Inorganic arsenic speciation analysis of water samples by trapping arsine on tungsten coil for atomic fluorescence spectrometric determination

Arsine trapping on resistively heated tungsten coil was investigated and an analytical method for ultratrace arsenic determination in environmental samples was established. Several chemical modifiers, including Re, Pt, Mo, Ta and Rh, were explored as permanent chemical modifiers for tungsten coil on-line trapping and Rh gave the best performance. Arsine was on-line trapped on Rh-coated tungsten coil at 640 °C, then released at 1930 °C and subsequently delivered to an atomic fluorescence spectrometer (AFS) by a mixture of Ar and H2 for measurement. In the medium of 2% (v/v) HCl and 3% (m/v) KBH4, arsine can be selectively generated from As(III). Total inorganic arsenic was determined after pre-reduction of As(V) to As(III) in 0.5% (m/v) thiourea–0.5% (m/v) ascorbic acid solution. The concentration of As(V) was calculated by difference between the total inorganic arsenic and As(III), and inorganic arsenic speciation was thus achieved. With 8 min on-line trapping, the limit of detection was 10 ng L−1 for As(III) and 9 ng L−1 for total As; and the precision was found to be <5% R.S.D. (n = 7) for 0.2 ng mL−1 As. The proposed method was successfully applied in total arsenic determination of several standard reference materials and inorganic arsenic speciation analysis of nature water samples.