Hyphenation of flow injection on-line preconcentration and ICP-MS for the rapid determination of Ra-226 in natural waters

A novel, sensitive, and rapid method is developed for the preconcentration/separation of Ra-226 in natural waters using a flow injection (FI) design based on a sequential on-line ion exchange preconcentration coupled with ICP-MS. Ra-226 is extracted using an Ln resin (HDEHP) from the sample at pH 10.6 in the presence of ethylenediamine tetraacetic acid ( EDTA) diammonium salt, whereas Ca and Mg, which form stable complexes with EDTA, are not retained on the column. Quantitative elution of Ra-226 from the Ln resin is achieved using 5 M HNO3. The separation of Ra from Ba and Sr is subsequently performed by the selective retention of Sr and Ba on an Sr* Spec resin, placed between the Ln resin and the Apex-Q system. In addition to being accurate and rapid for Ra-226 determination, this method is effective in eliminating spectral ((SrBa)-Sr-88-Ba-138) and non-spectral (Ca, Mg) interferences. Using a 20 mL sample, a detection limit (3 sigma) of 457 fg L-1 ( 16.92 mBq L-1) was obtained with a sample throughput of 3.5 samples h(-1). The precision for 6 replicate measurements of 5 pg L-1 ( 185.18 mBq L-1) Ra-226 was better than 4%. The method was applied to the analysis of natural waters, where the concentration of Ra-226 was found to be in the range 1.2 to 2.4 pg L-1 (44.4 to 88.8 mBq L-1), lower than the maximum acceptable concentration ( MAC) for Ra-226 of 16.2 pg L-1 ( 600 mBq L-1), recommended in the Guideline for Canadian Drinking Water Quality.