Application of ICP-QMS for the determination of ultratrace-levels of 226Ra in geothermal water and sediment samples

A rapid, accurate and less labor intensive approach to determining Ra-226 in environmental samples was examined; this utilized quadrupole-based inductively coupled plasma mass spectrometry (ICP-QMS). The procedure used chemical separation by ion exchange chromatography to remove most of the matrices after coprecipitation with BaSO4. The average chemical recovery of the NIST SRM preparation method ranged from 60.5 to 85.9% using Ba-133 as internal tracer by gamma counting. This technique was capable of completing a Ra-226 measurement within 3 min. It did not require an in-growth period to allow radon and its progeny to achieve secular equilibrium with the parent Ra-226 as is needed for liquid scintillation analyzer (LSA). The method detection limits for the determination of Ra-226 in geothermal water and sediment samples were 0.02 mBq L-1 (0.558 fg L-1) and 0.10 Bq kg(-1) (2.79 fg g(-1)), respectively. The results obtained with various natural samples and the suitability of the method when applied to various environmental matrices such as geothermal water and sediment are discussed. When ICP-QMS was compared to double-focusing magnetic sector field inductively coupled plasma mass spectrometry (ICP-SFMS), good agreement was obtained with a correlation coefficient, r (2) = 0.982.