Improving the analytical capabilities of femtosecond laser ablation multicollector ICP-MS for high precision Pb isotopic analysis: the role of hydrogen and nitrogen

Abstract

The effect of nitrogen and hydrogen addition to the central gas flow in femtosecond LA-ICP-MS has been investigated. Enhanced sensitivity of most elements was observed as a result of nitrogen and hydrogen addition to the Ar carrier gas before the ablation cell. Both gases resulted in decreased oxide ratios and increased abundances of doubly charged ions. The effect of nitrogen on sensitivity and mass bias of Pb isotopes in fs-LA-MC-ICP-MS was then investigated. The intensity of Pb and Tl was enhanced by a factor of 3–4 when nitrogen was mixed with Ar carrier gas. At the same time there was a systematic decrease in the mass bias (13%) of Pb and Tl with nitrogen addition. The mass bias of Tl is not identical to that of Pb but accurate and precise Pb isotope ratios were obtained when correcting for the mass bias difference. The results of this work indicate the usefulness of mixed gas plasma to improve signal intensities in ICP-MS in general and MC-ICP-MS in particular where large ion beams and robust and controlled mass bias corrections are necessary for precise and accurate isotopic analysis using Faraday detectors.