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

Abstract

The precise determination of radium-226 ( 226 Ra) 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 226 Ra 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 226 Ra 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 MnO 2 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 226 Ra 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.

Atomic spectrometry update – a review of advances in environmental analysis

“…The determination of 226 Ra was simplified 103 by replacing the standard R = 10 000 medium resolution slit of an ICP-SFMS instrument with a R = 2000 slit to ensure spectral peak separation from known interferents whilst maintaining a flat topped peak for good isotope ratio determinations. As the concentrations in seawater were expected to be between 0.03 and 0.1 fg g −1 , the 226 Ra was initially preconcentrated from 1 L of seawater by coprecipitation with MnO 2 and then isolated using a 2 column clean-up procedure (strong CEC followed by extraction chromatography).…”