Determination of technetium-99 in aqueous samples by isotope dilution inductively coupled plasma-mass spectrometry

An isotope dilution/inductively coupled plasma mass spectrometric method (ID/JCP-MS) for measuring the concentration of technetium-99 in aqueous samples was developed at the Savannah River Technology Center (SRTC). The procedure is faster than radiometric tecniques, is less subject to interferences, and has equal or better detection limits. It is currently being used to measure the concentration of Tc-99 in, samples of Savannah River water collected in the vicinity of the Savannah River Site. In this method one liter samples of water are spiked with Tc-97, After equilibration, the technetium is extracted from the sample with a chromatographic resin. Interfering elements, molybdenum and ruthenium, are either not retained by the resin or are washed off with dilute nitric acid. The technetium is then eluted with more concentrated nitric acid, and the Tc-99/Tc-97 ratio in the eluant is measured with an ICP-MS. The Tc-99 concentration in the original sample is calculated from the Tc-99/Tc-97,tio, The chemical recovery of the extraction procedure is greater than 90%. The detection limit of the instrument, taken as three times the background counts at m/z = 99, is 0.6 part per trillion (ppt). The detection limit of the procedure, taken as three times the standard deviation of several reagent blank analyses, is 0.33 pCi/l.