Determination of radium-226 in environmental samples by inductively coupled plasma mass spectrometry after sequential selective extraction

Abstract

A sequential selective extraction procedure for the pre-concentration of radium-226 in complex environmental matrices (i.e. uranium ores and biological samples) was developed and used in conjunction with an inductively coupled plasma collision cell quadrupole mass spectrometer (ICP-CC-Q-MS). In order to measure Ra-226 adequately by mass spectrometry, potential polyatomic interferences created by Ba, Ce, La, Nd, Pb and Sr (⁸⁸Sr¹³⁸Ba, ⁸⁷Sr¹³⁹La, ⁸⁶Sr¹⁴⁰Ce, ⁴⁰Ar⁴⁰Ar¹⁴⁶Nd, ¹⁸O²⁰⁸Pb), present at high concentrations in the matrix, had to be removed prior to the measurements. A combination of Sr*Spec and UTEVA cartridges was used to separate U, Sr, Pb and Ba from Ra. Subsequently, the eluate containing Ra was loaded onto a Ln cartridge to pre-concentrate Ra and separate it from interference created by Nd, La, and Ce. The entire extraction procedure took a few minutes compared to other Ra-226 chromatographic separations that take several hours. Using this protocol, an absolute detection limit of 0.02 fg (0.75 mBq) was obtained using less than 4 mg of solid sample or 25 mL of liquid sample. This procedure is very robust and can be used to analyze Ra-226 in a variety of matrices in the presence of several interferences.