Improving the utility of LA-ICP-MS for isotope ratio environmental science

New analytical capabilities enabling the analysis of smaller amounts of material lead directly to the development of new avenues of research in earth and environmental science. In-situ techniques such as laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and secondary ion mass spectrometry (SIMS) allow small amounts of material to be analysed (c.1-5ng) directly without the blank contribution from processing reagents which limit traditional dissolution-based methodologies. However, for materials of small size and/or low concentrations of analyte, the signal:noise ratio (SNR) limits the precision of the analysis. This dictates analysis of larger amounts of material to achieve the required precision, even for sensitive in-situ techniques. We intend to develop ground breaking laser ablation acquisition and data handling methods to routinely achieve higher SNR's and enhance precision. These methods will be applied to picogram-nanogram quantities of material, depending on the application. To demonstrate this capability, our primary application will be the uranium isotopic characterization of 1micron uranium oxide (UOx) particles for nuclear forensic investigations. This is an internationally important application with a pressing need to characterize individual micron-sized uranium particles collected during international monitoring operations. Isotope ratios from nuclear materials reveal details about their processing, origin, and purpose. Different degrees of enrichment from natural compositions (238U/235U = 137.88) are required for nuclear power (238U/235U to c.33) and nuclear weapons (238U/235U c. 1) whilst only minimal (c.0.13%) fractionation occurs in nature. Enrichment processes also produce equally disparate 236U/238U ratios. Uranium isotope ratios can therefore successfully fingerprint the source and ultimate origins of contaminant UOx particles. The challenge is therefore to analyse uranium isotope ratios from individual fine particles. Other techniques such as: alpha and gamma-ray spectrometry, fission-track, conventional thermal ionisation mass spectrometry (TIMS), SIMS and conventional solution multi-collector(MC-)ICP-MS, are either too time consuming and/or expensive, have low precision and/or resolution, or suffer from significant potential background and blank level limitations or interferences. Laser ablation MC-ICP-MS offers a potential solution for all applications requiring the analysis of low amounts of analyte, but only if new methodologies, such as those described here are developed. This proposal details how accurate quantification of isotope ratios in 1micron particles will be achieved using new analytical techniques such as laser ablation in liquid (LASIL), micro-volume ablation cell and torch technology, single pulse acquisition and total signal integration (TSI) data processing techniques. All these methods enhance SNR's and improve spatial resolution in mapping. LASIL combines the sampling benefits of LA with the SNR enhancement of solution mode analysis and offers the exciting possibility of in-drop single-bead post-ablation clean up and accumulation of material (where adequate sample is available) in a single drop to achieve a measureable concentration. The appropriate combination of all these approaches has the potential to successfully analyse 1micron particles and dramatically improve the spatial resolution and utility of LA-ICP-MS applied to environmental sciences. The student will benefit from training at NIGL, a world-class isotope geoscience laboratory, and integration at Loughborough, one of the UK's largest analytical science centres and one specialized in LA-ICP-MS science. The student will attend relevant modules of the MSc programme in Analytical Chemistry and Environmental Science at the University and participate in the graduate school training programme in transferrable and professional skills, also benefiting from annual reporting and progression vivas.