Determination of ultra-low 236U/238U isotope ratios by tandem quadrupole ICP-MS/MS

Isotope ratios of 236U/238U were measured at levels below 10-7 by single collector ICPMS with a tandem quadrupole mass separation mechanism. Peak tailing of the prominent 238U+ ion beam on the 236U+ peak was reduced to the level of ∼10-10 by use of two quadrupole mass filters. The 235UH+ interference on 236U+ was efficiently reduced to a UH+/U+ ratio of 1 × 10 -8 by an ion-molecule reaction between UH+ and O 2 in a collision/reaction cell placed between the two quadrupoles. The resultant detection limit for 236U/238U measurement was better than those reported by any other ICPMS study. The 236U/238U ratios, measured as 236U 16O+/238U16O+, were determined in the range 10-9 to 10-7 without correction for spectral interference. Accurate measurements of 236U/ 238U to as low as 1 × 10-10 are projected. © 2013 The Royal Society of Chemistry.