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

Abstract

A novel, sensitive, and rapid method is developed for the preconcentration/separation of ²²⁶Ra in natural waters using a flow injection (FI) design based on a sequential on-line ion exchange preconcentration coupled with ICP-MS. ²²⁶Ra 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 ²²⁶Ra 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 ²²⁶Ra determination, this method is effective in eliminating spectral (⁸⁸Sr¹³⁸Ba) and non-spectral (Ca, Mg) interferences. Using a 20 mL sample, a detection limit (3σ) 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) ²²⁶Ra was better than 4%. The method was applied to the analysis of natural waters, where the concentration of ²²⁶Ra 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 ²²⁶Ra of 16.2 pg L⁻¹ (600 mBq L⁻¹), recommended in the Guideline for Canadian Drinking Water Quality.