Determination of plutonium concentrations and isotope ratios in environmental samples with a double-focusing sector field ICP-MS

An analytical method for the ultratrace and isotopic analysis of plutonium in sediment samples using a double focusing sector field ICP mass spectrometer (ICP-SMS) is described. A detection limit for plutonium in the sub-fg ml−1 range was achieved. The ICP-SMS results were in acceptable agreement with alpha spectrometry. At the low fg ml−1 level a precision in isotope ratio measurements of 2–10% RSD was achieved. Accuracy of the results was assessed by 238U/235U and 205Tl/203Tl isotope ratio determinations using isotopic standards and a natural Tl standard solution, respectively. It was shown that correction for 238UH+ and 238UH+2 is necessary for both plutonium concentration and isotopic composition determinations. From a practical standpoint, the use of ICP-SMS for plutonium measurements is an attractive alternative to techniques such as alpha spectrometry and thermal ionization mass spectrometry (TIMS) due to its higher throughput and ability to measure both concentration and isotopic ratio on the same sample.