Radiostrontium and radium analysis in low-level environmental samples following a multi-stage semi-automated chromatographic sequential separation

Strontium isotopes, 89Sr and 90Sr, and 226Ra being radiotoxic when ingested, are routinely monitored in milk and drinking water samples collected from different regions in Canada. In order to monitor environmental levels of activity, a novel semi-automated sensitive method has been developed at the Radiation Protection Bureau of Health Canada (Ottawa, Canada). This method allows the separation and quantification of both 89Sr and 90Sr and has also been adapted to quantify 226Ra during the same sample preparation procedure. The method uses a 2-stage purification process during which matrix constituents, such as magnesium and calcium that are rich in milk, are removed as well as the main beta-interferences (e.g., 40K, 87Rb, 134Cs, 137Cs, and 140Ba). The first purification step uses strong cation exchange (SCX) chromatography with commercially available resins. In a second step, fractions containing the radiostrontium analytes are further purified using high-performance ion chromatography (HPIC). While 89Sr is quantified by Cerenkov counting immediately after the second purification stage, the same vial is counted again after a latent period of 10–14 days to quantify the 90Sr activity based on 90Y ingrowth. Similarly, the activity of 226Ra, which is separated by SCX only, is determined via the emanation of 222Rn in a 2-phase aqueous/cocktail system using liquid scintillation counting. The minimum detectable concentration (MDC) for 89Sr and 90Sr for a 200 min count time at 95% confidence interval is 0.03 and 0.02 Bq/L, respectively. The MDC for 226Ra for a 100 min count time is 0.002 Bq/L. Semi-annual intercomparison samples from the USA Department of Energy Mixed Analyte Performance Evaluation Program (MAPEP) were used to validate the method for 89Sr and 90Sr. Spiked water samples prepared in-house and from International Atomic Energy Agency (IAEA) were used to validate the 226Ra assay.