2-STEP COPRECIPITATION METHOD FOR DIFFERENTIATING CHROMIUM SPECIES IN WATER FOLLOWED BY DETERMINATION OF CHROMIUM BY NEUTRON-ACTIVATION ANALYSIS

A two-step method for the determination of CrVI and CrIII in natural waters was developed. The method is based on the variation of the coprecipitation yields with Pb(PDC)2 (PDC = pyrrolidine dithiocarbamate) as a function of pH. By using two different pH values both species can be determined separately. Firstly, CrVI was coprecipitated at pH 4.0 and the CrIII was separated at pH 9. Total chromium was determined by reduction of CrVI followed by coprecipitation at pH 9. The validity of the procedure was checked with the National Institute of Standards and Technology Standard Reference Material 1643b Trace Elements in Water and the result was found to be in good agreement with the certified value.