Bioassay and Environmental Analyses by Liquid Ion Exchange

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Abstract
Liquid ion exchange has replaced several solid ion exchange and extraction procedures at the Savannah River Plant (SRP). The principal advantage of the method is rapidity; many ions exchange from one liquid phase to the other within a few seconds. Separation procedures are relatively simple; an acidic aqueous sample is mixed with an equal volume of liquid ion exchange reagent diluted in an inert solvent. The cation exchanger is di-2-ethylhexyl phosphoric acid (HDEHP) and the anion exchanger is tri-isooctylamine (TIOA). The ion exchange characteristics of 37 elements were determined. Variations in exchangers, acid concentrations and stripping solutions resulted in separation of specific radionuclides from environmental and bioassay samples. HDEHP and TIOA are used to separate radionuclides with similar gamma energies prior to spectro-metric analyses. A complex mixture of Ce141, 144 and Np239, Cr51 and I131, Co58 and Ba140 + La, for instance, which previously required 24 hr. for analysis, can now be separated and analyzed in 1 hr. TIOA is a more efficient absorber of all forms of iodine than chloroform, the commonly used iodine absorber. TIOA is also used instead of tributyl phosphate extraction for alpha emitters. Many cations exchange to HDEHP from dilute acid solutions and this technique is used to concentrate radionuclides from environmental and bioassay samples.