Hydride interference on the determination of minor actinide isotopes by inductively coupled plasma mass spectrometry

Abstract

Hydrogen adducts of the major naturally occurring actinide isotopes ²³²Th and ²³⁸U were studied using an inductively coupled plasma mass spectrometer. The hydride:atomic ion ratios for both elements varied as a function of the parameters that were studied, i.e., nebulizer flow rate, solution uptake rate and desolvation conditions. When the instrument sensitivity for U and Th was optimized, ²³²ThH⁺:²³²Th⁺ was found to be (3.9 ± 0.2)× 10^–5 with pneumatic nebulization and (2.10 ± 0.07)× 10^–5 with ultrasonic nebulization. Under the same conditions, ²³⁸UH⁺:²³⁸U⁺ was found to be (3.2 ± 0.2)× 10^–5 and (1.8 ± 0.1)× 10^–5 using pneumatic and ultrasonic nebulization, respectively. Conditions that reduced hydrogen number density and/or increased plasma temperature decreased the hydride:atomic ion ratio. Such conditions are best if²³³U and ²³⁹Pu are to be determined in the presence of ²³²Th and ²³⁸U.