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

Abstract

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.