Cadmium analysis by radiochemical neutron activation analysis

Radiochemical neutron activation analysis (RNAA) has been routinely used at the National Bureau of Standards to analyze Cd in a variety of environmentally important matrices. The method used to separate Cd from other neutron-activated products is solvent extraction. Zinc diethyldithiocarbamate [Zn(DDC)2] in chloroform will quantitatively extract Cd from an aqueous solution over a pH range from 1 to 12. In addition to the extraction of Cd, Zn(DDC)2 will also extract Cu, which can interfere with the Cd analysis by producing a high background level of radiation. This can be avoided by first extracting with Bi(DDC)3 in chloroform which removes Cu, but not Cd. Copper concentrations can, therefore, be determined in addition to Cd. This two extraction radiochemical separation procedure is very versatile and is often used as part of a larger multi-element analysis scheme. One such scheme involves the use of an inorganic-ion exchanger, Hydrated Manganese Dioxide (HMD), to retain As, Sb, Se, and Cr prior to extraction. The eluted fraction is then extracted with Bi(DDC)3 to remove Cu, and then with Zn(DDC)2 to remove Cd.