Recent Developments in the Analysis of Techetium-99

Abstract

In recent years the use of extraction chromatography has grown significantly in methodologies for technetium-99 measurement. An aliphatic quaternary amine, impregnated on a polymeric support, trade named TEVA Resin has become a standard in separating and pre-concentrating pertechnetate prior to technetium-99 measurement by liquid scintillation or ICP-MS. TEVA Resin has a very high affinity for pertechnetate anion from low acid and even basic solutions. Figure 1 shows the uptake of TcO4 as a function of nitric acid and HCl concentration. It can be seen that the TcO4 uptake increases with decreasing acid concentration, while all the actinide elements show declining retention. This behavior indicates that the TEVA Resin can be used to separate pertechnetate anion from a wide variety of potentially interfering radionuclides. The k’ values in the range of 10–10 show that the resin can be used to pre-concentrate pertechnetate from very large volume samples (e.g. up to 4 liters of water.) The technique has been applied to a variety of matrices including water, soil, urine and waste samples. It has also been applied to process control samples in nuclear fuel reprocessing and waste treatment applications. TEVA Resin has been used in several formats: slurry-packed columns for gravity flow use, dry packed cartridges for us in vacuum manifold systems, and glass fiber filter discs to process very large liquid samples with fast flow rate (~100 mL/min.) As this methodology has been applied to broader and broader sample types, several challenging matrix interferences have been encountered that have made accurate measurements difficult. One example of a matrix challenge is the effect of high levels of Th-234 present in natural uranium samples on the quantitation of Tc-99 in the sample. In this case, the beta emissions from the interfering isotope are measured in the Tc99 window of the LSC. This can lead to a bias in the measurement of Tc-99.