Atomic fluorescence determination of inorganic arsenic in soils after microwave-assisted distillation Original Research Article

An inexpensive microwave-assisted distillation procedure has been developed for quantitative determination of inorganic arsenic in soils by atomic fluorescence spectrometry (AFS). After reduction of As(V) to its trivalent state with potassium iodide, inorganic arsenic was distilled as AsCl3 that was finally determined by atomic fluorescence after hydride generation with NaBH4 in HCl medium. The different parameters that control the distillation: concentration and volume of HCl, time of distillation, sample weight, and oven load, were studied. The methodology developed has a detection limit of 0.015 μg l−1, which corresponds to a concentration of 0.006 μg of As per gram of soil, and a relative standard deviation of 3% for nine independent analyses of the same soil sample containing 8.7 μg g−1 As. The recovery percentage of As(III) and As(V) were 103 ± 4 and 106 ± 4%, respectively. Total arsenic was determined after microwave-assisted digestion, under pressure, with HCl : HNO3 (3 : 1)/H2O2 in hermetically sealed Teflon reactors. By introducing an additional microwave-assisted digestion step after distillation of inorganic arsenic, the organic fraction of arsenic in soils and sediments was established.