MSFIA-LOV system for ²²⁶Ra isolation and pre-concentration from water samples previous radiometric detection

An automatic system based on multisyringe flow injection analysis (MSFIA) and lab-on-valve (LOV) flow techniques for separation and pre-concentration of ²²⁶Ra from drinking and natural water samples has been developed. The analytical protocol combines two different procedures: the Ra adsorption on MnO₂ and the BaSO₄ co-precipitation, achieving more selectivity especially in water samples with low radium levels. Radium is adsorbed on MnO₂ deposited on macroporous of bead cellulose. Then, it is eluted with hydroxylamine to transform insoluble MnO₂ to soluble Mn(II) thus freeing Ra, which is then coprecipitated with BaSO₄. The ²²⁶Ra can be directly detected in off-line mode using a low background proportional counter (LBPC) or through a liquid scintillation counter (LSC), after performing an on-line coprecipitate dissolution. Thus, the versatility of the proposed system allows the selection of the radiometric detection technique depending on the detector availability or the required response efficiency (sample number vs. response time and limit of detection). The MSFIA-LOV system improves the precision (1.7% RSD), and the extraction frequency (up to 3 h⁻¹). Besides, it has been satisfactorily applied to different types of water matrices (tap, mineral, well and sea water). The ²²⁶Ra minimum detectable activities (LSC: 0.004 Bq L⁻¹; LBPC: 0.02 Bq L⁻¹) attained by this system allow to reach the guidance values proposed by the relevant international agencies e.g. WHO, EPA and EC. - Highlights: • Automatic, rapid and selective method for ²²⁶Ra extraction/pre-concentration from water. • MSFIA-LOV system performs a sample clean-up prior to ²²⁶Ra radiometric detection. • ²²⁶Ra sample preparation allows using two radiometric detectors (LBPC and LSC). • Environmental levels of ²²⁶Ra are easily quantified. • High sensitivity and selectivity are achieved, reaching the ²²⁶Ra regulations for drinking water.