Determination of traces of uranium and thorium in (Ba, Sr)TiO3 ferroelectrics by inductively coupled plasma mass spectrometry

Traces of uranium and thorium in barium(II), strontium(II) titanate ((Ba, Sr)TiO3) ferroelectric materials were determined by inductively coupled plasma mass spectrometry (ICP-MS). Samples were completely dissolved by a mixture of 1.4% H2O2 and 1.0 mol.l(-1) HNO3. For a complete separation of the analytes from the matrix elements, a two step separation technique involving leaching and anion-exchange was applied. By the leaching step with HNO3 more than 90% of the matrix can be removed whereas the analytes completely remained in the solution. The anion-exchange step was carried out on a BIO.RAD AG1-X8 column with a mixture of 1.0 mol.l(-1) HF and 0.5 mol.l(-1) HNO3 as eluent. The content of uranium and thorium was subsequently measured by ICP-MS. The detection limits (D.L.) obtained were 0.043 ng g(-1) and 0.035 ng g(-1) for U and Th, respectively. The reproducibility was satisfactory with a relative standard deviation of less than 3% (at the 1 ng g(-1) level, n = 5). The matrix concentrations in the final solution were reduced to the sub-mu g ml(-1) level which is in the range of the detection limits of USN-ICP-AES (ultrasonic nebulization-ICP-atomic emission spectroscopy). The method was successfully applied to the determination of uranium and thorium in three synthetic (Ba, Sr)TiO3 samples spiked with the analytes at levels of 1, 5 and 10 ng g(-1) and three (Ba, Sr)TiO3 ferroelectric samples containing sub-ng g(-1) levels of the analytes.