Indirect spectrophotometric determination of arsenic(III) based on solid-phase extraction

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A new method for the indirect spectrophotometic determination of arsenic was developed. This method is based on the extraction of arsenic(III) from a solution of pH 1.5 on a finely divided anion-exchange resin as a complex with ammonium pyrrolidinedithiocarbamate(APDC), separation of the resin fixing the As(III)-APDC complex from the bulk solution on a membrane filter, re-dispersion of the resin in a solution containing copper(II) and conversion a coloreless As(III)-APDC complex to a yellow Cu(II)-APDC complex, collection of the rsin on a membrane filter and measurement of the absorbance of the resulting Cu(II)-APDC complex in the resin phase by a spectrophotometer or a densitometer. The effects of interfering ions were successfully suppressed with the combined use of diethyldithiocarbamate(DDTC) and EDTA. The method was applied to a standard river water sample. Good results were obtained for the detemination of arsenic(III,V) at the ppb level in 40ml of the sample.