My recent visit to the NEIF-RCF at East Kilbride near Glasgow was to help develop suitable methods for the compound-specific radiocarbon dating of individual fatty acids (FAs) and fatty acid methyl esters (FAMEs). The aim of this work generally is to enable more accurate age estimations of the Antarctic stomach oil deposits I am working on as a key part of my ERC funded PDRA position at Durham University. The compound-specific radiocarbon dates will both help improve chronologies and may help understand the extent of Antarctic water mass changes over the Holocene.
As part of NEIF commissioning the facility here at East Kilbride has recently purchased an innovative GC-MS and FID equipped with a large sample size injector and fraction collector, which is a critical part of the sample purification process.
Dr Josanne Newton (NEIF Senior Technician) has been actively trialling the system over the past few months and has amassed a great deal of technical knowledge, which together with her 14C expertise will be invaluable for the project. A key aim of my visit was to help pass on practical geochemistry GC-MS experience and help with the identification of C14, C16 and C18 fatty acids/FAMEs for which we hope to fraction collect over the next few months. Together we have been exploring the instrumentation and chromatograms (data which shows when each fatty acid is released from the device) to better understand how we might collect suitable quantities of sample for 14C-AMS dating.
Vital to the calculation of compound-specific 14C dates is the preparation and processing of appropriate standards. We started reviewing the 14C dates of some snow petrel stomach oils, we know from previous dates to be radiocarbon dead (older than approx. 50,000 14C years). Repeated dates taken from this deposit confirmed the entire deposit to be composed of old carbon and so makes this deposit suitable for use as an old radiocarbon depleted standard. I also brought from Durham extracts of modern apple peel samples to act as modern FA and FAME standards which we think we can separate effectively with the new equipment.
We also realised that if we are radiocarbon dating fatty acid methyl esters, we will be introducing an additional methyl group which contains carbon, which will need correcting the mass balance calculation. Therefore, we have prepared methanol we are using for radiocarbon dating. This was the first time we both prepared liquid samples for 14C dating and it involved cryogenically freeing samples in liquid nitrogen which was very exciting!
We have made great progress in the understanding of the new system and have been creating a plan for future work, which includes development of GC programs for collection of the required compounds and the assessment of blanks.
Overall, I have had an exciting week at the lab, and look forwards to the results of many 14C ages currently in the pipeline. I am excited to revisit to take part in the weighing of collected samples and the transfer of samples for further radiocarbon dating. Let’s hope we can collect large enough fractions for excellent ages!
Thank you Josanne, Philippa and NEIF-RCF for hosting me this week.
Mark Stevenson
29/07/22
