Towards online ramped oxidation (ORO)-AMS for thermal dissection and serial radiocarbon analysis of complex organic matter

Abstract By constraining organic carbon (OC) turnover times and ages, radiocarbon ( 14 C) analysis has become a crucial tool to study the global carbon cycle. However, commonly used “bulk” measurements yield average turnover times, masking age variability within complex OC mixtures. One method to unravel intra-sample age distributions is ramped oxidation, in which OC is oxidized with the aid of oxygen at increasing temperatures. The resulting CO 2 is collected over prescribed temperature ranges (thermal fractions) and analyzed for 14 C content by accelerator mass spectrometry (AMS). However, all ramped oxidation instruments developed to date are operated in an “offline” configuration and require several manual preparation steps, hindering sample throughput and reproducibility. Here we describe a compact, online ramped oxidation (ORO) setup, where CO 2 fractions are directly collected and transferred for 14 C content measurement using an AMS equipped with a gas ion source. Our setup comprises two modules: (i) an ORO unit containing two sequential furnaces, the first of which holds the sample and is ramped from room temperature to ∼900°C, the second of which is maintained at 900°C and holds catalysts (copper oxide and silver) to ensure complete oxidation of evolved products to CO 2 ; and (ii) a dual-trap interface (DTI) collection unit containing two parallel molecular sieve traps, which alternately collect CO 2 from a given fraction and handle its direct injection into the AMS. Initial results for well-characterized samples indicate that 14 C content uncertainties and blank background values are like those obtained during routine gas measurements at ETH, demonstrating the utility of the ORO-DTI setup.