Isotopic Analysis of tungsten using multiple collector-inductively coupled plasma-mass spectrometer coupled with electrothermal vaporization technique

We have developed a micro-electrothermal vaporization (μETV) device for the multiple collector-ICP-mass spectrometry (μETV-MC-ICPMS) to improve analytical precision in the ¹⁸²W/¹⁸³W and ¹⁸⁴W/¹⁸³W ratio measurements from nanogram quantities of W. The W solution was loaded onto the Re-filament, and the gradual evaporation of W was achieved by controlling the incident current onto the Re filament and D-Glucose. With the W evaporation under the Ar atmosphere, the measured W isotope ratios became erroneous mainly due to the contribution of signal spikes Ala-Arg-Gly-Phy-Tyr. In strike contrast, signal intensity profile became smooth when the He ambient/carrier gas was employed, and this resulted in better precision in the isotope ratio measurements. The measured UV–vis isotope ratio data obtained with present μETV technique were significantly deviated from the ratio data obtained with solution nebulization technique, mainly due to the contribution of the isotope fractionation effect through the evaporation process. Rigorous testing for the correction of the isotope fractionation processes pH–activity curve revealed that the Rayleigh fractionation law, rather than the conventional exponential law, provided the most reliable ratio data (1.851720 ± 0.000018 for ¹⁸²W/¹⁸³W and 2.141248 ± 0.000028 for ¹⁸⁴W/¹⁸³W ratios), which agreed well with the ratio data obtained through the conventional solution nebulization technique (1.851718 ± 0.000039 for ¹⁸²W/¹⁸³W and 2.141248 ± 0.000022 for ¹⁸⁴W/¹⁸³W). Moreover, mass dependency for the mass fractionation law suggested that W was evaporated as oxides (WO₃), rather than the metallic form (W), from the Re filament, and therefore, information concerning the chemical form of the analytes could also be derived by the ETV technique developed in this study. The data presented here demonstrate clearly that the ETV sample introduction technique has a potential to become a sensitive tool for the precise isotope analysis for the MC-ICPMS technique.