The automation and optimization of solid phase extractioninductively coupled plasma mass spectrometry analysis for the high throughput determination of aqueous levels of U, Th, Np, Pu, and Am

Abstract

The development of an automated chemical and mechanical sequence is presented for actinide analysis by inductively coupled plasma mass spectrometry (ICP-MS) using a column-based chromatographic system with TRU resin for matrix separation. The approach yields a robust method that allows for simple handling with high sample throughput for use in rapid response scenarios. Nanogram-level studies were carried out using ICP-MS with mono-isotopic spiked samples. Sample throughput was extrapolated to successfully handle over 2000 samples a day. This process includes a manual valency adjustment allowing for direct optimal loading while simultaneously minimizing sample dilution, an automated solid phase extraction platform, and a unique transfer system for flow through from the extraction to the ICP-MS detection platform. Bed volumes, reagent compositions, resin environments as well as volume and flow rates were optimized to increase recovery. Under optimal conditions the average recoveries over the range from 0.1 to 1.0 μg L⁻¹ were ²³⁸U 106.3 ± 5.4%, ²³⁷Np 100.5 ± 2.3%, ²⁴²Pu 94.3 ± 5.2% and ²³²Th 109.2 ± 4.8%. Using synthetic urine as a complex matrix the recoveries were ²³⁸U 96.2 ± 1.6%, ²³⁷Np 95.4 ± 1.7%, ²⁴²Pu 81 ± 2.4%, ²³²Th 98.8 ± 1.7% and ²⁴¹Am 53 ± 3.6% for samples at the 1 μg L⁻¹ level co-eluted with a 0.5 M HCl/0.3 M oxalic acid solution. These high recoveries were obtained while successfully removing 99.999% of monitored matrix ion constituents and minimizing reagent volumes, culminating in the development of a method that allows for rapid onsite handling of a large number of samples while maintaining high recovery and consistency inherent to automation.