Construction and evaluation of As(V) selective electrodes based on iron oxyhydroxide embedded in silica gel membrane

Two As(V) selective electrodes (with and without inner reference solution) have been developed using selective membranes based on iron oxyhydroxide embedded on silica gel mixed with ultrapure graphite at a 2/98 (w/w) ratio. The active component of the membrane was synthesised by means of the sol-gel technique and characterized by X-ray and FTIR spectroscopy. This compound shows a great affinity towards As(V) ions adsorbing 408 mg g−1. Using 1 mol l−1 phosphate buffer (at a 1/1, v/v ratio) to adjust the pH and the ionic strength to 7 and 0.5 mol l−1, respectively, the calibration curve is linear from 1.0 × 10−1 to 1.0 × 10−6 mol l−1 As(V), with a practical detection limit of 4 × 10−7 mol l−1 (0.03 mg l−1) and a slope close to 30 mV decade−1. The effect of potentially interfering ions was investigated. The accuracy and precision of the procedure have been tested on arsenic-free drinking water samples spiked with known amounts of arsenic and on groundwater samples containing high levels of arsenic. Total arsenic in these samples was determined after oxidation of As(III) with iodine at pH 7. The results of total As were comparable to those generated by ET-AAS.