Isotopes and science: my student placement at BGS

In chemistry student Dorontina Domi’s first couple of months of her placement at BGS, she has rotated between different laboratories including organics, collagen extraction and modern environmental gas analysis. This has provided her with a broad experience of the different instruments and sample preparation techniques that are required within BGS’s Stable Isotope Facility (SIF). In this blog, Dorontina tells us about some of her experiences so far. 

Carbon and nitrogen isotopes in organic materials

A wide array of instruments in the SIF can be used to analyse the carbon (C) and nitrogen (N) isotope composition of organic materials found in sediments, soils and plant materials. The bulk of the analysis is carried out using an Elementar isoprime precisION isotope ratio mass spectrometer (IRMS) with a vario ISOTOPE cube elemental analyser (EA). The samples are combusted in the EA and are then passed onto the IRMS on a continuous flow of helium carrier gas, selected for its inertness and separation efficiency for measurement.

While learning sample preparation, I gained experience in using microbalances to weigh samples down to 200 micrograms (or 0.0002 grams), which is a miniscule amount that is challenging to see with the naked eye. I compacted the weighed sample material into either crucibles or capsules, depending on the instrument and their auto sampling methods.

When analysing these sample materials for C isotopes, it is important to understand whether the results are representing organic or inorganic C fractions contained in the material. Organic carbon consists of compounds sourced from living organisms and their remains, and inorganic carbon, such as from carbonates, is formed from biological and geological processes. The two forms of C have very distinct isotope compositions (inorganic C typically has more carbon-13 compared organic C) and even a small amount of inorganic C contamination in samples can offset target organic C isotope values.

Samples must therefore be treated to remove inorganic C prior to isotope analysis. I acidified samples using hydrochloric acid (HCl) and rinsed them with purified water, using a centrifuge to ensure thorough washing, until the pH tested neutral. This process dissolves the inorganic C fraction and isolates the organic C fraction.

SIF houses 13 mass spectrometers, so I have also gained experience in how staff conduct maintenance, such as on the Elementar IRMS. I assisted in replacing the consumables to ensure that the analyses are performed with a high precision and accuracy.

Carbon, nitrogen and sulfur isotopes in prehistoric bone samples

Comparing carbon, nitrogen and sulfur isotope ratios from carnivores and their prey allows us to distinguish the palaeo-diet of animals and the trophic level structure of different species. This allows us to interpret their relationships during different ages and draw inferences from the data on changes associated with climate differences. For example, the higher the nitrogen isotope composition (δ¹⁵N) the more ‘carnivore-like’ feeding habits took place, therefore the main prey for each species can be identified.

Statistical tools called Bayesian mixing models will be used as a framework to integrate the large proportion of data from throughout modern and Pleistocene times and to infer the relevant data. Through this, the project will assess how changes in climate and environment influenced the feeding behaviour of the wolves and their resilience during reductions in prey availability. This information is crucial to understand the influence climate change will have on the endangered species in the future and help conservation strategies.

As part of the sampling programme, I was given an opportunity to spend a day at the Natural History Museum laboratories in London, where I observed the meticulous drilling process used to cut small pieces of material from a variety of different fossil species for later analysis. The samples were cut from areas that will minimise damage of the structural integrity of the bone for conservation purposes.

As well as fossil samples, the project is also analysing contemporary wolves from Croatia and their prey as a comparison. These samples are less than 100 years old and required an initial solvent treatment in the geomicrobiology lab before collagen extraction could begin.

I have also helped to prepare the samples for isotope analysis, where a multi-step process takes place to extract the collagen, before it is purified and analysed via the EA-IRMS.

Carbon isotopes in methane samples

Another aspect of my training covers analysing methane (CH₄) gas samples for their carbon isotope composition using a Sercon HS2022 with CyroGas.

This instrument works by purifying the sample gas via carbon dioxide (CO₂) traps and a cryogenic gas trap to remove any other sources of carbon present that are not from CH₄, thus reducing potential sources of contamination. The sample gas then flows through a combustion tube, where the CH₄ is converted to CO₂ and cryogenic trapping takes place, ensuring that the CO₂ is concentrated in the final trap and can be released to the mass spectrometer rapidly. This allows for a narrow, sharp peak that can be analysed and replicated with a high precision. I also hope to help with the analysis of hydrogen (H) isotopes via the pyrolysis of CH₄ to H₂.

Working at BGS as a student

If you are an undergraduate student looking for an opportunity within stable isotopes, I highly recommend BGS. Not only is it the largest UK producer of stable isotope data, but it is also a supportive workplace to be a part of. There are a variety of clubs to involve yourself in such as the BGS Wilding Group. Staff and volunteers maintain the natural areas at BGS to promote wildlife biodiversity, as a commitment to sustainability.

I would like to extend a massive thank you to everyone at the Stable Isotope Facility for welcoming me with such support and excitement. It has been an incredible start to the placement and I am looking forward to the rest of the year!

About the author 

Dorontina Domi is an undergraduate chemistry student at the University of Surrey, completing her industrial placement at SIF, which is located at BGS’s headquarters in Keyworth, Nottinghamshire.