A New UV Oxidation Setup for Small Radiocarbon Samples in Solution

Abstract

The requirements of extracting minute amounts of organic carbon in solution with high yield and minimum background are a prerequisite for radiocarbon dating of microgram amounts of carbon. Samples for biomedical or environmental research often arrive at the accelerator mass spectrometry (AMS) lab as concentrates dissolved in 1 mL of water or less. We have developed a new extraction method based on photo-oxidation by ultraviolet (UV) light. The solution is transferred into UV-transparent quartz vials with a head volume of pure oxygen and UV from low-pressure mercury discharge lamps is applied. To exclude the introduction of carbon background, we avoid any additional oxidizing agents. Under these conditions, only the 185 nm line is considered effective. To characterize the yield and the background, we have investigated artificial samples prepared from different materials. The setup developed allows parallel oxidation of 9 samples within typically 2 hr, connected directly to our graphitization setup for extremely small samples. The method was applied successfully for a study on dissolved organic carbon (DOC) in ice from 26 Austrian glaciers. A special advantage of the UV oxidation method in this case was that phosphoric acid could be used to remove carbonates, while its low vapor pressure prevented complete lyophilization. We see the most promising field of application in biomed research and compound-specific analysis.