Accurate determination of selenium in blood serum by isotope dilution analysis using inductively coupled plasma collision cell mass spectrometry with xenon as collision gas

Abstract

A method for accurate selenium determination in blood serum by isotope dilution analysis (IDA) was developed. Selenium was determined by ICP octopole reaction system MS using xenon as the collision gas (130–160 μL min⁻¹) in order to eliminate polyatomic interferences from argon, chlorine, phosphorus and bromine. The detection limit was 3.3 μg L⁻¹, which was higher than with hydrogen (0.4 μg L⁻¹) but sufficiently sensitive to determine selenium in serum. Selenium isotope ratios could be determined precisely and accurately without any mathematical interference corrections, enabling IDA at the ⁸⁰Se/⁷⁶Se ratio. In contrast, these corrections were necessary when hydrogen was used as the reaction gas due to the formation of SeH⁺ (2.4%) and BrH⁺ (14%), but even then systematic errors in the correction of the BrH⁺ interference could not be avoided. Hence, the selenium recovery from human serum reference material was only 78.0 ± 0.4% when measured with hydrogen but 96.7 ± 4.0% with xenon.