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

Lead Research Organisation: University of Bristol
Department Name: Chemistry

Abstract

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.

Planned Impact

Compound-specific d15N determinations, are difficult to achieve with high accuracy and precision. The Bristol group has spent over 25 years developing novel analytical approaches, both in terms of experimental design and analysis, such that it is an internationally recognised centre-of-excellence for 15N-SIP and compound-specific d15N determinations. Provision of an automated, high sensitivity platform will enable a step-change in sample throughput and support on-going and future innovation of 15N-based methodologies. The academic and societal impacts (see below) have the potential to be profound and far reaching. Academic impact shall be conducted through the usual routes of dissemination (papers, conference presentations and grant generation and tracked with Research Fish). Wider societal impact shall be encouraged through media promotion, out-reach events and engagement with public/private institutions responsible for policy and other activities that are impacted by the N-cycle.

As the limiting nutrient in soil, sustainable and environmentally ethical management of N is critical to future food security. 15N-SIP studies directly inform about key elements of the N-cycle (e.g. biological nitrogen fixation, abiotic/biotic transformation of N-forms and hydrological N-transport) and underpin soil use management in the agricultural sector. Furthermore, development of key chemical sensors for N-processes shall provide a novel, non-invasive means of assessing soil N health. The use of 15N as a determinant for trophic hierarchies shall help inform about community shifts in ecosytems wrought by climate change and other stressors such as pollution, thereby helping drive environmental policy. Finally, the asset shall generate new insights for archaeologists and historians into the activities and cultural development of mankind through better constraint of diet and associated economic and social development.

The asset will be transformative for UoB researchers as it will hugely increase capacity to study N-cycling in the environment both in terms of sample turnover and, importantly, size of sample and the types of compounds that can be targeted. Greater understanding of hitherto obscure and poorly understood aspects of the N-cycle has the potential to underpin high impact outputs. In particular, more efficient use of N in the agricultural sector, better characterisation of largely unknown organic matter in the hydrological cycle and previously unobtainable diet reconstructions in palaeoecology and, contemporaneously, trophic hierarchies/behaviours in the face of climate change. Research undertaken by the OGU, its collaborators (UoB and external) and users of NEIF-B answers to research objectives across the entire NERC remit and as such the asset could not be better placed to support impactful NERC science benefitting students/researchers/academics across, not just one, but multiple different research programmes. It is anticipated that impact shall be further evidenced through new collaborations and grant awards led by the University of Bristol and facilitated by access through the South West Universities GW4 and NEIF-B. Immediate beneficiaries shall be University of Bristol researchers and, more widely, UK based researchers working within the scientific remit of NERC. Commercial exploitation of any spare capacity (should it arise) shall also be investigated through our extensive network of national and international collaborators and with support from UoB's business fellows. The asset is highly complementary to other molecular and isotope (13C, 14C, 2H) mass spectrometry capabilities that position the UoB as world leaders in this approach to biogeochemical research.

Publications

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