Uranium-lead isotopic analysis from transient signals using high-time resolution-multiple collector-ICP-MS (HTR-MC-ICP-MS)
206Pb/238U isotopic ratios were measured from transient signals produced by laser ablation of short time period (4 shots with 60 kHz repetition rates). To investigate the effect of dwell time on measured ratio measurement, signal intensities of 206Pb and 238U were obtained with various dwell times (200, 20, 2, 0.2, 0.1, 0.04, and 0.02 ms). The signal intensities of 206Pb and 238U increase with shortening the dwell time, and the resulting peak signal intensities of 238U for three zircons (Plešovice, GJ-1, and Nancy 91500) exceeded 106 cps with the shortest dwell time (0.02 ms), and the signal intensities decreased with longer dwell times (2–200 ms). This is mainly due to moderation of the signal intensity of 238U through averaging the intensity data from neighboring time slices, suggesting that the measured signal intensity profile was not reflect the actual signal intensities. Based on the moderated signal intensity data, correction of the counting loss due to detector dead time can be erroneous, and this can be well demonstrated by the changes in the measured 206Pb/238U ratios among the data acquisition with different dwell times. With the correction of the counting loss based on data obtained the short dwell time (0.02 ms), the resulting 206Pb/238U ratios for zircon and glass standard materials were in good agreement with the literature within the analytical uncertainties achieved in this study (2–3%). The data obtained here demonstrate clearly that the acquisition with short dwell time is essential to obtain reliable elemental/isotopic data from transient signals emanating from single-shot laser ablation and introduction of nanoparticles.