A rapid throughput technique to isolate pyrogenic carbon by hydrogen pyrolysis for stable isotope and radiocarbon analysis. (28th February 2020)

• Record Type: Journal Article
• Authors: Haig, Jordahna; Ascough, Philippa L.; Wurster, Christopher M.; Bird, Michael I.
• Is Part Of: Rapid communications in mass spectrometry. Volume 34:Number 10(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-02-28
• Subjects: Mass spectrometry -- Periodicals; 543.65
• DOI: 10.1002/rcm.8737
• Languages: English
• ISSNs: 0951-4198

Abstract

Abstract : Rationale: Rapid, reliable isolation of pyrogenic carbon (PyC; also known as char, soot, black carbon, or biochar) for the determination of stable carbon isotope ( δ 13 C) composition and radiocarbon ( 14 C) dating is needed across multiple fields of research in geoscience, environmental science and archaeology. Many current techniques do not provide reliable isolation from contaminating organics and/or are relatively time‐consuming. Hydrogen pyrolysis (HyPy) does provide reliable isolation of PyC, but the current methodology is time consuming. Methods: We explored the potential for subjecting multiple samples to HyPy analysis by placing up to nine individual samples in custom‐designed borosilicate sample vessels in a single reactor run. We tested for cross‐contamination between samples in the same run using materials with highly divergent radiocarbon activities (~0.04–116.3 pMC), δ 13 C values (−11.9 to −26.5‰) and labile carbon content. We determined 14 C/ 13 C using accelerator mass spectrometry and δ 13 C values using an elemental analyser coupled to a continuous flow isotope ratio mass spectrometer. Results: Very small but measurable transfer between samples of highly divergent isotope composition was detectable. For samples having a similar composition, this cross‐contamination is considered negligible with respect to measurement uncertainty. For samples having divergent composition, we found that placing a sample vessel loaded with silica mesh adsorbent between samples eliminated measurable cross‐contamination in all cases for both 14 C/ 13 C and δ 13 C values. Conclusions: It is possible to subject up to seven samples to HyPy in the same reactor run for the determination of radiocarbon content and δ 13 C value without diminishing the precision or accuracy of the results. This approach enables an increase in sample throughput of 300–600%. HyPy process background values are consistently lower than the nominal laboratory process background for quartz tube combustion in the NERC Radiocarbon Laboratory, indicating that HyPy may also be advantageous as a relatively 'clean' radiocarbon pre‐treatment method.