Continuous online determination of ²²⁶Ra in liquid effluents using automated column chromatography-ICP-MS

Abstract

A measurement system capable of continuous on-line matrix removal, pre-concentration and analysis of 226Ra using pre-packed columns coupled to a flow injection system and an ICP-MS was developed. Full instrumental control of both the ICP-MS and the flow injection system provided automatic integration of the transient signals. The flow injection system was programmed to control column conditioning, sample loading, column rinsing, analyte elution and column cleaning operations employing appropriate solutions. The application of this system to the 226Ra analysis of an industrial liquid effluent was demonstrated. Using this particular instrument together with pre-concentration and matrix removal procedures, a limit of detection of 5.4 fg L−1 (2 mBq L−1) and a method detection limit of 16.2 fg L−1 (6 mBq L−1) were achieved for the measurement of 226Ra using a 25 mL sample volume. Total time for sample handling and analysis is approximately 10 minutes. The concentration of 226Ra in a discharged effluent sample was 0.73 pg L−1 (27 mBq L−1), which is in good agreement with the value of 0.81 pg L−1 (30 mBq L−1) measured using conventional alpha counting techniques.

High Throughput, Direct Determination of 226Ra in Water and Digested Geological Samples

“…Despite being mentioned as an important interference in several studies, , 88 Sr 138 Ba + did not cause an interference in any of the gas modes tested here. Interferences from W and Pb caused relatively high BEC for 226 Ra (up to 520 pg L –1 ) in both no gas and He mode, as seen by others, , but were below the limit of detection in N 2 O mode.…”

“…Despite being mentioned as an important interference in several studies, 12,16 88 Sr 138 Ba + did not cause an interference in any of the gas modes tested here. Interferences from W and Pb caused relatively high BEC for 226 Ra (up to 520 pg L −1 ) in both no gas and He mode, as seen by others, 15,16 but were below the limit of detection in N 2 O mode. Similar interference effects were observed for the solution with 61 different elements, i.e., measurable BEC (6−18 pg L −1 ) in no gas and He mode (MS) but below detection in N 2 O mode.…”

“…Several methods have been developed for concentration and separation of 226 Ra in samples before analysis by ICPMS, online or offline. ,,− , These methods are often more complicated than what is necessary before our detection method, as the reaction with N 2 O in the ICP-QQQ means that specific interferences, such as Sr and Ba that chemically follow Ra, do not need to be removed. To lower the detection limit of water samples with the presented method, a simple separation or concentration procedure, e.g., cation exchange separating monovalent from divalent cations, is thus expected to be sufficient.…”

“…Accelerator mass spectrometry (AMS), thermal ionization mass spectrometry (TIMS), and inductively coupled plasma mass spectrometry (ICPMS) have also been used for 226 Ra determination and offer faster analysis time than radioanalytical techniques. However, the developed methods still require tedious concentration and separation procedures prior to analysis in order to increase the Ra concentration and/or remove interferences. ,− ,− For measurements of 226 Ra by ICPMS, spectral interferences at m / z 226 can be caused by polyatomic ions like 88 Sr 138 Ba + , 186 W 40 Ar + , 207 Pb 19 F + , 208 Pb 18 O + and combinations of Mo and Xe isotopes. ,− …”

“…The detection limit was 1 Bq L −1 (∼27 pg L −1 ), which is insufficient for evaluating drinking water quality in the US or EU. Evans et al 16 did an online matrix removal with column chromatography before analysis with ICPMS, achieving a LOD of 0.05 pg L −1 for treated mine effluent samples in a 10 min procedure, but preparations and troubleshooting are normally more timeconsuming for such a system than for direct measurements with ICPMS. Another option for online removal of interferences with ICPMS is the use of a reaction gas such as O 2 , NH 3 , or N 2 O.…”