Quantification of 234Th recovery in small volume sea water samples by inductively coupled plasma mass spectrometry

• Main Authors: S. M. Pike, K. O. Buesseler, J. Andrews, N. Savoye
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2005
• Subjects: Southern Ocean
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.554.6988; http://cafethorium.whoi.edu/TEXT/234Th Recovery JNRC.pdf

Development of a small volume (2-4l) technique for measuring 234Th in sea water has been instrumental in bringing to light small-scale structures in upper-ocean particle removal processes previously missed by standard 234Th measurement techniques. Further development of this method to evaluate removal efficiencies of 234Th via MnO2 precipitation quantified using ICP mass spectrometry are presented in this work. Advantages to this approach are precise knowledge of 234Th recovery, while maintaining high sample throughput afforded by ICP-MS analyses. The improved technique includes the acidification of 4-l sea water samples and the addition of 230Th as a yield monitor prior to MnO2 precipitation. Subsequent filtration and beta counting of the high-energy daughter, 234mPa, was followed by a final background count after 6 half-lives (144 days) of decay. Filtered precipitates were dissolved with H2O2, and an internal standard of 229Th was added. Samples were purified using anion exchange chromatography to remove high levels of manganese, and recoveries were determined by measured ratios of 230Th/229Th by ICP-MS. Application of this procedure for 234Th derived export in the recent Southern Ocean Iron Experiment showed average recoveries of 91%. Corrections for rare low recoveries (25-80%) noticeably change 234Th profiles, thus impacting subsequent elemental flux calculations.