Carbonate removal from radiocarbon samples using a “no leach” acid pretreatment to retain mobile organic carbon

Abstract Inorganic carbon can be a significant contaminant of radiocarbon samples. It usually occurs in the form of carbonate which must be removed prior to measurement of the organic carbon fraction in a sample. This can be achieved by an acid wash, however, this approach results in the loss of mobile organic carbon components and is therefore unsuitable for situations where all organic carbon in a sample should be retained for measurement (e.g., carbon cycle studies). An alternative approach to retain mobile organic carbon while removing carbonate is fumigation using concentrated acid, however, this can inadvertently cause the loss of acid-labile organic carbon and modify the chemical composition of organic matter (as shown by changes to the thermal profile). Here, we present our “no leach” method which is designed to maximize carbonate removal from samples, while minimising the loss of organic carbon. The method incorporates a test via an inexpensive CO 2 sensor to confirm complete decarbonation, allowing a reduction in the required volume and molarity of acid, therefore, mitigating some of the issues commonly associated with other approaches to remove carbonate from a mixed sample. We present results for standards and samples which confirm the utility and reliability of this approach for radiocarbon measurement of a range of sample types.