Sequential measurement of δ¹⁵N, δ¹³C and δ³⁴S values in archaeological bone collagen at the Scottish Universities Environmental Research Centre (SUERC): A new analytical frontier

Abstract

Rationale:The use of multi-isotopic analysis (δ 15 N, δ 13 C and δ 34 S values) of archaeological bone collagen to assist in the interpretation of diet, movement and mobility of prehistoric populations is gradually increasing, yet many researchers have traditionally avoided investigating sulphur due to its very low concentrations (<0.3%) in mammalian collagen. For this reason, and as a consequence of analytical detection limits, sulphur is usually measured separately from carbon and nitrogen, which leads to longer analytical times and higher costs. Methods:A Thermo Scientific™ EA IsoLink™ isotope ratio mass spectrometry (IRMS) system, with the ability to rapidly heat a gas chromatography (GC) column and concentrate the sample gas online without cryo-trapping, was used at the Radiocarbon Laboratory at the Scottish Universities Environmental Research Centre (SUERC). Optimisation of the GC temperature and carrier gas flow rate in the elemental analyser resulted in improved signal-to-noise (S/N) ratio and sensitivity for SO 2 . This allowed for routine sequential N 2 , CO 2 and SO 2 measurements on small samples of bone collagen.Results: Improvements in sample gas transfer to the mass spectrometer allows for sequential δ 15 N, δ 13 C and δ 34 S values to be measured in 1-1.5 mg samples of bone collagen. Moreover, the sensitivity and S/N ratio of the sample gas, especially SO 2 , is improved, resulting in precisions of ±0.15‰ for δ 15 N values, ±0.1‰ for δ 13 C values and ±0.3‰ for δ 34 S values. Previous instrumentation allowed for the analysis of~30 unknown samples before undertaking maintenance; however, 150 unknown samples can now be measured, meaning a 5-fold increase in sample throughput. Conclusions:The ability to sequentially measure δ 15 N, δ 13 C and δ 34 S values rapidly in archaeological bone collagen is an attractive option to researchers who want to build larger, more succinct datasets for their sites of interest, at a much-reduced analytical cost and without destroying larger quantities of archaeological material.

Radiocarbon chronology and environmental context of Last Glacial Maximum human occupation in Switzerland

“…For stable isotope analysis, 1.2-1.5 mg aliquots of purified collagen were weighed into tin capsules and analysed using a Delta V Advantage continuous-flow isotope ratio mass spectrometer coupled via a ConfloIV to an EA IsoLink elemental analyser (Thermo Fisher Scientific, Bremen) at the Scottish Universities Environmental Research Centre (SUERC). For every ten unknown samples, three in-house standards that are calibrated to the International Atomic Energy Agency (IAEA) reference materials USGS40 (L-glutamic acid, δ 13 C VPDB = -26.4‰, δ 15 N AIR = -4.5‰), USGS41 (L-glutamic acid, δ 13 C VPDB = +37.6‰, δ 15 N AIR = -47.6‰), USGS43 (Indian Human Hair: δ 15 N AIR = +8.44‰, δ 13 C VPDB = -21.28‰, δ 34 S VCDT = +10.46‰), IAEA-S-2 (silver sulfide, δ 34 S VCTD = +22.7‰), and IAEA-S-3 (silver sulfide, δ 34 S VCTD = -32.3‰) were analysed 76 . Results are reported as per mil (‰) relative to the internationally accepted standards VPDB, AIR and VCDT.…”

Sulfur isotope analysis of cysteine and methionine via preparatory liquid chromatography and elemental analyzer isotope ratio mass spectrometry

“…Sayle et al 19 observed large (0.6‰ per V) size‐related errors for aliquots of bone collagen analyzed for δ 34 S with the same model of EA/IRMS system. In our tests with SO 2 reference gas, performed daily prior to analyses, linearity effects were consistently low (<0.1‰ per V).…”

“…42,43 3. bone collagen also using a single reactor. 19 Without additional copper in the second reactor, however, there is potential for incomplete NO x conversion into N 2 , which was not explicitly tested for in their study.…”

“…18 Most recently, the Thermo Scientific Flash EA-Isolink equipped with a temperature-ramped chromatographic column was used to measure δ 34 S in bone collagen samples containing just 2-3 μg sulfur. 19 This system, which we improved upon in the current study, provides sufficient sensitivity to make offline preparative isolation of the sulfur AAs much less tedious.…”

Magdalenian and Epimagdalenian chronology and palaeoenvironments at Kůlna Cave, Moravia, Czech Republic

“…N 2 , CO 2 , and SO 2 entered the mass spectrometer via an open split arrangement within the ConfloIV and were analysed against their corresponding reference gases. For every ten archaeological samples, three in-house standards that are calibrated to the International Atomic Energy Agency (IAEA) reference materials USGS40 (L-glutamic acid, δ 13 C VPDB = -26.4‰, δ 15 N AIR = -4.5‰), USGS41 (Lglutamic acid, δ 13 C VPDB = + 37.6‰, δ 15 N AIR = -47.6‰), IAEA-CH-6 (sucrose, δ 13 C VPDB = -10.5‰), IAEA-N-1 (ammonium sulphate, δ 15 N AIR = + 0.4‰), IAEA-S-1 (silver sulphide, δ 34 S VCTD = -0.3‰), IAEA-S-2 (silver sulphide, δ 34 S VCTD = 22.7‰), IAEA-SO-5 (barium sulphate, δ 34 S VCTD = 0.5‰), and IAEA-SO-6 (barium sulphate, δ 34 S VCTD = -34.1‰) were run (Sayle et al 2019). Results are reported as per mil (‰) relative to the internationally accepted standards VPDB, AIR, and VCDT.…”