Micro-extraction procedures for the determination of Ra-226 in well waters by SF-ICP-MS

Abstract

The radium-226 ( t 1/2 = 1622 years) content of highly alkaline well water collected from the United Arab Emirates (UAE) was measured by double focusing sector-field inductively coupled plasma-mass spectrometry (SF-ICP-MS) after separation of the radium from other alkaline earth elements using a newly developed procedure. The results were comparable with those obtained by α-spectrometry for samples with concentrations ranging from 6.75 to 459 pg/L (0.25 to 17 Bq/L). Instrumental sensitivity on matrix-free samples was compared for two sample introduction systems, i.e. an Apex-Q high sensitivity system and a concentric nebulizer. A 12-fold improvement in sensitivity (instrumental detection limit = 1.5 pg/L or 55 mBq/L) was found when the Apex-Q system was used. Two chromatographic methods were tested for the sequential separation of the alkaline earth elements contained in the well water samples in order to reduce matrix and polyatomic interference effects. Optimal elution parameters were determined and used for the separation and pre-concentration of Ra-226 in those samples. A method detection limit of 0.189 pg/L (7 mBq/L), which corresponds to a mass of 0.38 fg of Ra-226 in the sample, was achieved. Only 2 mL of sample is necessary when a combination of 50 W-X8 and Sr*Spec resin, which are reusable, are utilized for the separation. This new analytical protocol significantly reduces sample preparation time resulting in a throughput rate of approximately 20 samples in only 8 h; faster than the other published extraction procedures.