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

A method for the determination of trace amounts of arsenic and tin in natur al waters is described. Trace amounts of arsenic and tin were preconcentrat ed by coprecipitation with a Ni-ammonium pyrrolidine dithiocarbamate (APDC) complex. The coprecipitates obtained were directly analyzed by graphite-fu rnace atomic-absorption spectrometry (GFAAS) using the Ni-APDC complex soli d-sampling technique. The coprecipitation conditions used for the trace amo unts of arsenic and tin in natural water were investigated in detail. It wa s found that arsenic and tin at sub-ng mL(-1) levels were both coprecipitat ed quantitatively by Ni(PDC)(2) in the pH range 2-3. The concentration fact ors by coprecipitation reached approximately 40,000 when 2 mg nickel was ad ded 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 f or 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.