Radiocarbon analysis is an indispensable tool in various fields, including environmental studies, archaeology, geochemistry, and marine science. Two primary oxidation methods for solids, elemental analyzer combustion (EAC) and closed tube combustion (CTC), are routinely used to prepare samples for 14C analysis. While both have been validated with international reference materials, a comprehensive comparison of these two methods using diverse, real-world environmental samples is currently lacking. We conducted such a comparison, analyzing the fraction modern (F14C) values across a range of environmental matrices. For the majority of the samples, the results from both methods were in good agreement. However, we observed a significant F14C discrepancy of up to 30% between the two methods for low-carbon concentration samples (<1% by weight). While intrinsic heterogeneity of organic matter in environmental samples complicated interpretation, this finding suggests that the prolonged combustion time of the CTC method can be important for ensuring complete oxidation for samples containing heat resistant organic matter, given the growing popularity of automated EAC in radiocarbon laboratories.
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