Effects of ionic radiological and chemical interferences on the chromatographic separation of a radionuclide standard solution

For characterizing radioactive samples there are two major considerations in the application of a coupled liquid chromatography and on-line scintillation counting system: (1) radiological interferences and (2) chemical interferences from the matrix. A study was conducted to identify which interferences from typical matrices found at several Department of Energy facilities affected the separation of a radioactive tracer solution by the coupled system. The selection of potential interferent materials was determined through a review of characterization and monitoring studies of surface water, ground water, and high level waste tank supermatant at those facilities. Incremental mass loadings of contaminant were mixed with a standardized radioactive tracer (⁵⁵Fe,⁶³Ni,⁹⁰Sr and¹⁴⁷Pm) and then injected into a coupled system. The resultant chromatograms were compared to the chromatogram of the standard radionuclide solution to determine the effects of the chemical or radiological constituent. Relative to the radionuclide solution,¹³⁷Cs was the only activation/fission product used in this study to effect a radiological interference. For the natural uranium series, a radiological interference was observed for⁹⁰Sr due to either a uranium isotope or a decay product of the series. No rad interference was observed from²²⁸Th, though it must be noted that the elution program was not capable of completely separating the decay series nuclides of natural uranium or thorium. For the chemical interferences, the effects are twofold since the chemical can affect the concentration of ions on the pre-concentration stage as well as the chromatographic separation. The general trend observed was that increasing the ionic strength of the chemical resulted in decreased retention fractions on the pre-concentration column and significant shifts in peak elution times.