This study established two modes for Pb isotope ratio analysis:the Faraday cup-ion counter(FC-IC)and the Faraday cup(FC),based on the Pb contents of analyzed samples.Since 206Pb,207Pb,and 208Pb were all analyzed using FC detectors in both modes,the 2RSE(two-times relative standard error)of the 20yPb/206Pb(y=7,8)ratios was consistent and was only related to the 208Pb signal intensity.Under the same 208Pb signal intensity(within the IC linear range),the 2RSE of 208Pb/204Pb in the FC-IC cup mode is higher than that in the FC cup mode,and the 2RSE difference of 208Pb/204Pb between the two modes decreases with the increase of 208Pb signal intensity,with the lowest 2RSE being approximately 0.06%.Better precision and accuracy of the Pb isotope ratios can be achieved when the 208Pb signal intensity is>0.50 V in the FC cup mode and between 0.10 V and 0.25 V in the FC-IC cup mode.For samples with relatively high Pb contents(>40 μg/g)or big sizes,better precision can be obtained using the FC cup mode.In contrast,for samples with lower Pb contents(≈10 μg/g)or small sizes,the FC-IC cup mode can provide better precision.Pb isotopic analyses of geological reference glasses with different Pb contents were conducted using the established micro-area in-situ Pb isotopic analytical method,and the results were consistent with the reference values within errors.
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