Improving Precision and Accuracy of Isotope Ratios from Short Transient Laser Ablation-Multicollector-Inductively Coupled Plasma Mass Spectrometry Signals: Application to Micrometer-Size Uranium Particles

The isotope drift encountered on short transient signals measured by multicollector inductively coupled plasma mass spectrometry (MC-ICPMS) is related to differences in detector time responses. Faraday to Faraday and Faraday to ion counter time lags were determined and corrected using VBA data processing based on the synchronization of the isotope signals. The coefficient of determination of the linear fit between the two isotopes was selected as the best criterion to obtain accurate detector time lag. The procedure was applied to the analysis by laser ablation-MC-ICPMS of micrometer sized uranium particles (1-3.5 mu m). Linear regression slope (LRS) (one isotope plotted over the other), point-by-point, and integration methods were tested to calculate the U-235/U-238 and U-234/U-238 ratios. Relative internal precisions of 0.86 to 1.7% and 1.2 to 2.4% were obtained for U-235/U-238 and U-234/U-238, respectively, using LRS calculation, time lag, and mass bias corrections. A relative external precision of 2.1% was obtained for U-235/U-238 ratios with good accuracy (relative difference with respect to the reference value below 1%).