2009 Volume 2009 Pages 73-80
A fully-automated (FA) technique applying 207Pb-204Pb double spike (DS) to thermal ionization mass spectrometry (TIMS) has been developed (FA- DS- TIMS). A long-term baseline is measured prior to the sample measurement runs and is applied to all of the acquired sample data, avoiding sample wasting caused by frequent baseline measurements during sample runs. FA- DS- TIMS offers reliable fully automated sequential analyses of 10 samples in one batch, including 10 natural runs and 10 runs doped with a spike enriched 207Pb and 204Pb. This cuts operating labor costs, although the measurement time is longer than a conventional TIMS or an identical run using multi collector-inductively coupled plasma-mass spectrometry (MC-ICP-MS).
The isotopic ratios of the 207Pb-204Pb double spike used in this study are 206Pb/204Pb = 0.10203, 207Pb/204Pb = 3.8717 and 208Pb/204Pb = 0.18865 when normalized to NIST SRM 982 208Pb/206Pb = 1.00016. Average values for NIST SRM 981 containing 7.5 and 15 ng Pb are 206Pb/204Pb = 16.9390 ± 0.0017, 207Pb/204Pb = 15.4972 ± 0.0017, 208Pb/204Pb = 36.7213 ± 0.0045 (errors are 2SD, n = 12). These are within error of recently reported values obtained by DS-TIMS and DS-MC-ICP-MS. The reproducibility of 208Pb/204Pb in this study is 0.003% using 15 ng Pb, and 0.009% using 7.5 ng Pb. These are similar to, or better than, those reported by various other methods. The average values for JB-2 containing 20ng Pb are 206Pb/204Pb = 18. 3419 ± 0. 0027, 207Pb/204Pb = 15.5622 ± 0.0026, 208Pb/204Pb = 38.2814 ± 0.0078 (errors are 2SD, n = 5) and are comparable to those reported in recent studies. These results show that the new technique is reliable in terms of both accuracy and precision.
