Simultaneous AMS determination of 14C content and total carbon mass in biological samples

Abstract

Abstract Accelerator Mass Spectrometry (AMS) is now recognized as one of the most powerful techniques available for conducting ultrasensitive clinical studies. However, since for biological applications the relevant quantity is the total 14 C activity (i.e. dpm/mL sample), AMS 14 C measurements must be combined with total carbon concentrations measured on a separate instrument using a different sample aliquot. This procedure is inherently a source of large inaccuracies, especially in non-homogeneous samples such as urine and fecal blends. To overcome this limitation we developed a new measurement technique whereby a small amount of 13 C-enriched carbon carrier is added to each sample. Accurate measurement of the 13 C/ 12 C and 14 C/ 13 C ratios of the mix can be used to simultaneously calculate total carbon mass and 14 C concentration of the original sample. In this paper we present our first test runs including a detailed error analysis demonstrating that sample mass and 14 C concentration of the original sample can be determined with a precision and accuracy of better than 3%, thus significantly reducing the final uncertainty due to sample in-homogeneities.