Integrating Continuous-Flow Mass Spectrometry and Automatic CO₂ Collection for AMS

Abstract

Accelerator mass spectrometry (AMS) radiocarbon measurements of organic samples require combustion to obtain CO 2 for graphitization. Furthermore, determination of δ 13 C values is required in order to correct the 14 C age due to carbon isotope fractionation effects. δ 13 C analysis is commonly carried out by stable isotope mass spectrometry because most applications demand high-precision δ 13 C values in addition to the requirements of 14 C dating. A simplifying step is therefore to combine the combustion for stable isotope analysis with cryogenic trapping of CO 2 for AMS graphite targets. Presented here is a simple CO 2 trapping device based on a modified Gilson 220XL sampling (manifold) robot coupled to the inlet manifold system of a GV Instruments IsoPrime stable isotope mass spectrometer. The system is capable of batch combustion and analysis of up to 40 samples and is under full computer control by the mass spectrometer software. All trapping parameters such as flush time prior to trapping and total trap time are adjustable through the standard software user interface. A low 14 C activity of background materials and high precision and accuracy of stable isotope analysis of carbon and nitrogen are demonstrated.