New Method for the Determination of Ra-226 in Natural Waters
Brooks Applied Labs (BAL) recently developed a new method utilizing ion chromatography coupled to an ICP-MS for the quantification of radium (226Ra). This novel analytical approach can achieve detection limits low enough to provide meaningful data for natural water samples with low background radiation levels.
226Ra is a product of the 238U decay series and is the longest-lived isotope of radium, with a half-life of 1602 years. It is one of the most toxic natural radioelements, owing to its high specific activity of 1 pCi/pg, compared with that of 238U at 3 pCi/g. Determination of trace levels of 226Ra is usually carried out by radiometric methods (alpha spectrometry, gamma-ray spectrometry, liquid scintillation counting, etc.). These methods usually require significant sample preparation before analysis, either to preconcentrate 226Ra or to remove the interfering isotopes. In addition, lower detection limits usually require very large sample volumes (> 500 mL) as well as radiometric counting times in the order of days.
Inductively coupled plasma – mass spectrometry is usually not the first choice for this application, as the concentration of Ra in most samples (< 0.740 Bq/L) is less than the detection limit of most current ICP-MS systems. The new BAL method uses ion chromatography coupled to a Nexion 350D ICP-MS to achieve a 0.009 Bq/L detection limit. This method allows common interferences such as 88Sr138Ba+, 87Sr139La+, 86Sr140Ce+, 208Pb18O+, 186W40Ar+, 209Bi16O1H+, and 88Sr138Ba+ (as well as matrix ions such as Ca and Mg) to be chromatographically separated and requires only a 5-mL sample volume. The analytical method was validated by comparing the results of natural water samples using various methods, including alpha spectrometry.
The BAL method is an excellent alternative to common radiometric methods, especially in emergency situations, as it utilizes common instrumentation and provides rapid turnaround time (as fast as 48 hours) for results with comparable or lower detection limits. BAL is a DOECAP-audited laboratory available to perform specialty trace metals analytical services at all US DOE sites and maintains a current Radioactive Materials License.
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