Simultaneous measurements of As, Mo, Sb, V and W using a ferrihydrite diffusive gradients in thin films (DGT) device

The ferrihydrite-backed DGT (diffusive gradients in thin films) recently developed for arsenic and phosphate measurements was for the first time characterized with respect to molybdate antimonate vanadate and tungstate determination Arsenate was included in the characterization to allow comparison with literature data and thus provide quality control of the measurements In addition to laboratory experiments field measurements were carried out in a natural stream in northern Sweden affected by mine drainage It was shown that ferrihydrite-DGT is suitable for simultaneous determination of labile arsenic molybdate antimonate vanadate and tungstate over a wide pH range Diffusion coefficients were estimated using two different methods diffusion cell and direct uptake to DGT devices in synthetic solutions Estimations of the coefficients using the direct uptake method were performed between pH 4 and 8 The results from the two methods agreed well irrespective of pH except for molybdate and antimonate that showed decreased values at pH 8 Adsorption of the analytes to ferrihydrite gel-discs was rapid at all pH values However there was a tendency toward lower adsorption affinity for antimonate compared to the other anions 100% recovery of accumulated analytes was achieved through complete dissolution of the ferrihydrite adsorbent using 1 4 mol L-1 HNO3 with 0 1 mol L-1 HF From field sampling it was concluded that the opportunities for accurate antimonate and molybdate determination decrease at pH >= 8 7 DGT-labile concentrations were generally lower than dissolved concentrations Relatively lower DGT concentrations compared to dissolved (<0 45 mu m) were observed under a period when ferric oxide precipitations were detected on the DGT protective filter (C) 2010 Elsevier B V All rights reserved