The analysis of 226Ra in 1-liter seawater by isotope dilution via single-collector sector-field ICP-MS

The precise determination of radium-226 (Ra-226) in environmental samples is challenging due to its low concentration. Seawater typically contains between 0.03 and 0.1 fg g(-1 226)Ra. Thus, this work addresses the need for an easy and precise methodology for Ra-226 determination in seawater that may be applied routinely to a large number of samples. For this reason, a new analytical approach has been developed for the quantification of Ra-226 in seawater via inductively coupled plasma mass spectrometry (ICP-MS). Analysis by single collector sector-field ICP-MS was shown to be convenient and reliable for this purpose once potential molecular interferences were excluded by a combination of chemical separation and intermediate mass resolution analysis. The proposed method allows purification of Ra from the sample matrix based on preconcentration by MnO2 precipitation, followed by two-column separation using a cation exchange resin and an extraction chromatographic resin. The method can be applied to acidified and unacidified seawater samples. The recovery efficiency for Ra ranged between 90% and 99.8%, with precision of 5%, accuracy of 95.7% to 99.9%, and a detection limit of 0.033 fg g(-1) (referring to the original concentration of seawater). The method has been applied to measure Ra-226 concentrations from the North Sea and validated by analyzing samples from the central Arctic (GEOTRACES GN04). Samples from a crossover station (from GEOTRACES GN04 and GEOTRACES GN01 research cruises) were analyzed using alternative methods, and our results are in good agreement with published values.

Automated summary

A new analytical approach using ICP-MS for the quantification of Ra-226 in seawater has been developed in this study. The method, which involves preconcentration by MnO2 precipitation and two-column separation using resins, showed high recovery efficiency, precision, and accuracy, with a low detection limit. The proposed method was successfully validated on samples from different regions and compared well with alternative methods used for analysis.