Determination of Uranium Isotopes using ICP-QQQ-MS
Naturally-occurring uranium has three isotopes: 234U, 235U, and 238U. 238U has the highest abundance at 99.3%. On the other hand, due to the uranium enrichment process, enriched uranium contains more 234U than natural uranium. Uranium enrichment is aimed at obtaining 235U; however, the process results in the concentration of the lighter isotopes. Uranium activity in waters is often determined by alpha spectrometry measuring 234U and 238U. Alpha spectrometry requires chemical separation before analysis, making sample preparation difficult and, therefore, increasing the total time per analysis.
Inductively coupled plasma mass spectrometry with triple quadrupole technology (ICP-QQQ-MS) is a very powerful analytical technique for the determination of uranium concentrations. It is not uncommon to achieve sub-parts-per-trillion detection limits for total uranium analysis, but more importantly, it is also an alternative to alpha spectrometry for the analysis of uranium isotopes.
Brooks Applied Labs has developed a new method for the determination of very low 234U, 235U, and 238U concentrations in most water samples. The sensitivity of the Agilent 8800 ICP-QQQ-MS, coupled with a front-end preconcentration system, allows us to determine even the lowest abundance isotope (234U at 0.005%) at sub-parts-per-quadrillion levels, corresponding to an activity level far below 1 mBq (0.027 pCi).