A dry ashing assay method for the trace determination of Th and U in polymers using inductively coupled plasma mass spectrometry

This paper discusses the methods developed for determining the radiopurity of high density polyethylene and polyetherketone ketone materials to be considered for use in ultralow background physics experiments. This work focuses on the processes used to render the polymeric samples acid soluble for subsequent ultratrace analysis using inductively coupled plasma mass spectrometry. High density polyethylene was determined to contain 2.19 ± 0.42 pg Th/g and 2.81 ± 0.52 pg U/g. The method provided very low absolute detection limits of 17.2 and 38.1 fg for Th and U, respectively. However, the polyetherketone ketone sample etched or devitrified the quartz, causing determined values to be a factor of 2–4 higher for Th and 5–9 higher for U from dissolution assay results.