Direct radiocarbon measurements of dissolved inorganic carbon from environmental water using a gas ion source 

An increasing demand for radiocarbon analysis of small samples has led to the development of various methods to further improve and simplify the CO2 extraction needed for accelerator mass spectrometer (AMS) measurements. Here, the performance of a direct feeding system of CO2 from dissolved inorganic carbon (DIC) from small water samples (<6 ml) and direct AMS measurement via a gas ion source coupled to a gas interface system (GIS) is presented and compared to the conventional preparation by graphitization that demands significantly larger samples (> 60 ml). Seawater samples collected from Sargasso Sea, southeast of and lake water samples collected from Lake Constance have been prepared by both methods. The extraction of CO2 gas from samples for GIS measurement is performed using a carbonate handling system (CHS-Ionplus AG) through purging the headspace, acidifying the water, and sparging out the CO2. The preparation time is greatly reduced compared to conventional analysis that requires the labor-intensive graphitization step. The yielded 14C results from the direct CO2 measurements are in good agreement with values obtained from graphite measurements. The observed deviation between the two methods is below the uncertainty of radiocarbon gas measurement (~7‰). This new approach will facilitate understanding of carbon cycle dynamics in many different environments and applications where a high throughput (up to 80 sample/day) is required. The new method is suitable for groundwater, pore water, seawater, freshwaters from lakes, rivers and glacial settings. Furthermore, it enables the analysis of small milliliter-scale samples and those containing low DIC concentrations.