GEOTRACES radium isotopes interlaboratory comparison experiment

• Published in: Limnology and oceanography, methods methods, 2012-06, Vol.10 (6), p.451-463
• Main Authors: Charette, Matthew A., Dulaiova, Henrieta, Gonneea, Meagan E., Henderson, Paul B., Moore, Willard S., Scholten, Jan C., Pham, M.K.
• Format: Article
• Language: English
• Subjects: Brackish; Marine
• ISSN: 1541-5856; 1541-5856
• DOI: 10.4319/lom.2012.10.451

In anticipation of the international GEOTRACES program, which will study the global marine biogeochemistry of trace elements and isotopes, we conducted a multi‐lab intercomparison for radium isotopes. The intercomparison was in two parts involving the distribution of: (1) samples collected from four marine environments (open ocean, continental slope, shelf, and estuary) and (2) a suite of four reference materials prepared with isotopic standards (circulated to participants as ‘unknowns’). Most labs performed well with 228Ra and 224Ra determination, however, there were a number of participants that reported 226Ra, 223Ra, and 228Th (supported 224Ra) well outside the 95% confidence interval. Many outliers were suspected to be a result of poorly calibrated detectors, though other method specific factors likely played a role (e.g., detector leakage, insufficient equilibration). Most methods for radium analysis in seawater involve a MnO2 fiber column preconcentration step; as such, we evaluated the extraction efficiency of this procedure and found that it ranged from an average of 87% to 94% for the four stations. Hence, nonquantitative radium recovery from seawater samples may also have played a role in lab‐to‐lab variability.