Preconcentration by coprecipitation of arsenic and tin in natural waters with a Ni-pyrrolidine dithiocarbamate complex and their direct determination by solid-sampling atomic-absorption spectrometry.

A method for the determination of trace amounts of arsenic and tin in natural waters is described. Trace amounts of arsenic and tin were preconcentrated by coprecipitation with a Ni-ammonium pyrrolidine dithiocarbamate (APDC) complex. The coprecipitates obtained were directly analyzed by graphite-furnace atomic-absorption spectrometry (GFAAS) using the Ni-APDC complex solid-sampling technique. The coprecipitation conditions used for the trace amounts of arsenic and tin in natural water were investigated in detail. It was found that arsenic and tin at sub-ng mL(-1) levels were both coprecipitated quantitatively by Ni(PDC)2 in the pH range 2-3. The concentration factors by coprecipitation reached approximately 40,000 when 2 mg nickel was added as a carrier element to 500 mL of the water sample. The proposed method has been applied to the determination of trace amounts of arsenic and tin in river water and seawater reference materials, and the detection limits for arsenic and tin, which were calculated from three times of the standard deviation of the procedural blanks, are 0.02 ng mL(-1) and 0.04 ng mL(-1), respectively, for 500-mL volumes of water sample.