Determination of extractable arsenic in soils using slurry sampling-on-line microwave extraction-hydride generation-atomic absorption spectrometry

A flow injection procedure has been developed for the determination of acid-extractable arsenic in soils by hydride generation atomic absorption spectrometry. Several parameters, including acid and borohydride concentrations, exposure time to microwave energy, and the microwave power applied, were optimized. The on-line microwave extraction increased the recovery of the adsorbed arsenic significantly; whereas, preparation of the slurry in 10% hydrochloric acid instead of water increased the recovery only when the microwave oven was off. Low recoveries, which were investigated by removing the hydride generation manifold and connecting the system via an on-line filter to an inductively coupled plasma mass spectrometer, were due to the irreversible adsorption of arsenic on the soil. This irreversible adsorption does not allow standard additions calibration. The solution detection limit was 0.2 μg l−1 for a 212-μl injection loop, corresponding to 7 ng g−1 in solid for a 2.5% m/v slurry prepared in 25 ml.