A coral 129I/127I measurement method using ICP-MS and AMS with carrier addition

[摘要] Iodine-129 in coral cores provides historical records of human nuclear activities, establishes or confirms coral age models, and traces environmental processes. At the time of this writing, the only published method (Biddulph et al., 2006) for measuring 129I/127(stable)I in corals required 10–30 g of sample, which can be too large for common practice. To reduce this sample size requirement, we modified the existing method in two aspects: (1) we used inductively coupled plasma mass spectrometry (ICP-MS) instead of an iodide selective electrode (ISE) for stable 127I measurement; and (2) we added 0.66 mg of a low-ratio (129I/127I = 1.5 × 10−14) iodine carrier instead of using a carrier-free method for target preparation for 129I measurement by accelerator mass spectrometry. For 127I measurement, we obtained the detection limit and limit of quantitation of 0.089 and 0.27 ppb, respectively, using a 133Cs internal standard, a 286× dilution factor, and drift correction. The average 127I concentration in corals was 4.5 ppm. For 129I/127I measurement, we determined the average anthropogenic (post-1950) and natural (pre-1950) ratios of 20 × 10−12 and 1.4 × 10−12, respectively, in our coral samples. In addition, the average relative standard deviations were 11.5% and 23% for anthropogenic- and natural-age coral samples, respectively. Our method successfully measured 129I/127I in 1–4 g of corals with accuracy and precision comparable to the existing method, which required 10–30 g of corals.

[学科分类] 分析化学