Precise measurement of 226Ra/230Th disequilibria in ocean sediments and porewater by high-sensitivity ICP-MS
Liuting Yuan 1,2, Xinyu Jiang 1,2, Pinghe Cai 1,2,*
1. State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen 361005
2. College of Ocean and Earth Science, Xiamen University, Xiamen 361005
The 226Ra/230Th isotope is a potential proxy for tracing solute exchange processes in the sediment-water interface in the deep sea. In order to use this proxy, we need to measure depth profiles of 226Ra/230Th in deep-sea sediments, porewater as well as overlying water. In this paper, we focused on the pretreatment, purification and measurement of Ra samples. Dry sediment samples (~0.2g) were digested before separation of Ra from Th using an 8 mL anion exchange resin column (AG1*8, 100-200 mesh). Primary separation of Ra and Ba from other matrix ions was accomplished using an 8 mL cation exchange resin (Bio-Rad 50W*X8, 100-200 mesh), followed by a 2.5 mL cation column to further purify Ra and Ba. Finally, a 0.5 mL strontium-specific resin was used to isolate Ra from Ba. Measurement of 226Ra was performed by high-sensitivity Inductively Coupled Plasma Mass Spectrometry (ELEMENT XR). This procedure can be applied to porewater and seawater samples, only requiring to change the digestion step to a manganese dioxide coprecipitation step. Eventually, we developed an analytical method for the precise measurement of 226Ra/228Ra ratios and 226Ra and 230Th concentrations in samples by high-resolution Element XR, which provided a small sample size (~0.5mL), high precision (<5%) and a short analytical time (~3 minutes) for the measurement.
Key words: 226Ra/230Th deep-ocean ICP-MS
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