Gas chromatograph-combustion-isotope ratio mass spectrometer (GC-C-IRMS) for enhanced compound-specific N isotope determinations

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This proposal will provide the necessary state-of-the-art capital to underpin multiple innovative methodologies (developed by the OGU) that will provide new, unrealised insights into the N-cycle across multiple NERC research themes, i.e food security, climate change, microbial, plant and animal ecology, palaeoecology and archaeology. For over twenty years, the OGU has committed itself to developing and improving analytical methodologies for the stable-N isotopic characterisation of organic compounds. This has led to the development and successful application of a compound-specific approach, that determines d15N values of individual AAs, in the burgeoning field of stable isotope ecology and archaeology. Determining d15N values for individual amino acids is extremely challenging, resulting in far lower sample throughput compared with d2H and d13C determinations, capabilities the OGU also possesses. The challenges arise for several reasons, which ultimately result in long set-up times and inherent analytical errors that result in the need for multiple analyses of every sample. Our long experience in the development and use of this technique has made the OGU one of the few laboratories, worldwide that can deliver this analytical capability with confidence (see O'Connell and Collins. 2018. J. Hum. Evol. 117, 53-55.). The compound-specific N isotope approach provides potentially unrivalled sensitivity and specificity for natural abundance and 15N-tracer determinations, unachievable by any other means, e.g. bulk EA-IRMS. There is now a strong upward trajectory in the uptake in use of this compound-specific stable-isotope technique in ecology, palaeoecology, archaeology and 15N-stable isotope probing (15N-SIP) biogeochemistry being undertaken by the OGU, other collaborators/users within UoB and in the wider national and international communities. The food-web ecology and terrestrial/aquatic biogeochemistry represent significant areas of NERC research, and it is accepted that compound-specific isotope approaches have significant advantages over bulk stable isotopic determinations. Demand is set to increase rapidly (see Academic beneficiaries), therefore, there is a an immediate and acute need to increase capacity to meet this increase in demand. Critically, the latest generation of GC-C-IRMS instruments, i.e. the proposed asset, offer significantly enhanced sensitivity compared to their predecessors (<1000 molecules/ion). This enhanced sensitivity will enable analyses to be performed at much lower sample concentrations with a higher throughput than possible using existing instruments. Crucially, this would enable us to expand the current analytical window to include lower mass samples (e.g. small macrofauna, sub-samples from high-value palaeoecological and archaeological specimens) allowing us to field a greater range of potential research applications within the NERC remit. As well lowering the limit of detection for AAs (compounds with naturally high molar ratios of N), the increased sensitivity of the asset will enable compounds with higher C:N ratios to be determined. This will enable aspects of the N-cycle, previously difficult, or even impossible to study, to become amenable to 15N-SIP determinations, thereby unlocking fundamental new insights into N-cycling processes (e.g. d15N values of nitrogenous bases and amino sugars in soil providing new insights into the activity and function of the soil bacterial and fungal communities). This deeper probing of complex environmental systems will help address key global problems, such as N use efficiency in agriculture and the exact nature of N-organic matter in aquatic systems.