A rapid throughput technique to isolate pyrogenic carbon by hydrogen pyrolysis for stable isotope and radiocarbon analysis

Abstract

RATIONALE: Rapid, reliable isolation of Pyrogenic Carbon (PyC; char, soot, black carbon; biochar) for 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 to employ. 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 to 116.3 pMC), δ 13 C values (-2 11.9 to-26.5‰) and labile carbon content. We determined 14 C/ 13 C by accelerator mass spectrometry and δ 13 C values by elemental analyser coupled to continuous flow isotope ratio mass spectrometer. RESULTS: Very small but measurable transfer between samples of highly divergent isotope composition was detectable. Where samples are of broadly similar composition, this cross contamination is considered negligible with respect to measurement uncertainty. Where samples are of divergent composition, it was 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. CONCLUSION: It is possible to subject up to seven samples to HyPy in the same reactor run for 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 pretreatment method.

The black carbon cycle and its role in the Earth system

“…13 C NMR yields different but complementary information about the aromaticity and condensation of BC. Hydrogen pyrolysis eliminates labile organic carbon from total organic carbon using thermochemical decomposition into gases in the absence of oxygen 178 , isolating samples for stable and radiocarbon analysis 179 . The weak nitric acid method isolates and quantifies the BC fraction in mineral soil samples 180 .…”

A radiocarbon chronology for Sanamere Lagoon, Cape York Peninsula, using multiple organic fractions

“…Other studies (e.g. Orr et al, 2021;Haig et al, 2020;Turney et al, 2021) support this conclusion. The ANSTO combustion-graphitisation blank at ANSTO laboratories in routinely determined for every studied batch of samples as described in Bird et al (2014), and the final results of this study were corrected based on these blank measurements.…”

Provenance of Aerosol Black Carbon over Northeast Indian Ocean and South China Sea and Implications for Oceanic Black Carbon Cycling

“…The concentrations and δ 13 C BC – Δ 14 C BC of BC in PM 2.5 were analyzed based on hydrogen pyrolysis (HyPy) technique. HyPy is a rapid/reductive method for BC isolation, quantitation, and isotope analysis, facilitating the removal of potential 14 C contamination while minimizing BC loss. − The dual-carbon isotope provinces of aerosol BC were identified based on their different δ 13 C BC – Δ 14 C BC signatures. Then, the provenance of aerosol BC in different isotope provinces was quantitatively explored by comprehensive analysis of the Bayesian model, backward trajectory model, metal element tracers, and estimates of BC emissions from shipping.…”