Isotope dilution analysis of yttrium with labelled oxygen gas by dynamic reaction cell-ICP-MS: universal isotope dilution analysis

A new Isotope Dilution (ID) method using a labelled reaction gas in ICP-DRC-MS has been established and a theoretical background for the method is given. The element of interest reacts with the labelled O2 in the reaction cell of the ICP-MS and is determined by measuring the intensity ratios of its monoxide ions with and without a third element in a similar way to a conventional ID method. The proposed ID method is applicable to the determination of monoisotopic elements as well as multiple stable isotopes. As an example, the approach was used for the determination of yttrium (Y). Yttrium reacted with 16O and 18O gas in the reaction cell to generate two yttrium–oxygen molecular ions (89Y16O and 89Y18O), and then, the signal intensity ratios of the two molecular ions with and without the third element (107Ag), whose mass number was the same as that of 89Y18O, were measured. The Y concentration was calculated from the intensity ratios measured at m/z = 105 and 107 and the mass abundances of 16O, 18O and 107Ag. Yttrium was determined in certified river water and fern. The determined Y concentration agreed with the certified value and/or with that determined using external calibration.