An automated ultracleanion exchange separation method for the determinations of 232Th and 238U in copper using inductively coupled plasma mass spectrometry

This work presents a novel analytical method for ultrasensitive (sub-pg g−1) determinations of Th and U in copper. The method is based on the use of clean sample preparation procedures and includes the use of an offline automated ion exchange separation method, followed by inductively coupled plasma mass spectrometric (ICP-MS) analysis. The separation system is equipped with a single reusable chromatographic column that, with the rigorously clean procedures developed herein, provided a low carryover, low background, and reproducible automated separation method. Isotope dilution methods were used for quantitation. Method Detection Limits (MDLs) of 3.7 and 9.4 fg g−1 were obtained for the quantitation of 232Th and 238U in copper, respectively, corresponding to activities of 0.0148 and 0.116 μBq kg−1 for 232Th and 238U, respectively. The analytical method provided high and reproducible tracer recoveries. The use of an automated system significantly reduced the tedious active work time required for the chemist (by ca. 80%) relative to manually performing the separation. This method could be adapted to other critical sample matrices requiring the utmost in high throughput clean chemistry procedures.