Submitted to: Radiocarbon
Publication Type: Review Article
Publication Acceptance Date: 11/1/2006
Publication Date: 12/1/2006
Citation: Getachew, G., Burri, B.J., Kelly, B., Buchholz, B.A., Vogel, J.S., Clifford, A.J., Kim, S., Haack, K.W., Ognibene, T.J., Modrow, J. 2006. HOW TO CONVERT BIOLOGICAL CARBON INTO GRAPHITE FOR AMS. Radiocarbon. Vol. 48(3) 325-336. Interpretive Summary: Radioisotopes are important tools for nutrition studies because they can track nutrients as they are metabolized and used throughout the body. However, most radioisotope methods cannot be used in people because high levels or radiation are dangerous. Fortunately there is a sensitive radioisotope method (accelerator mass spectrometry) that has been used for radiocarbon dating for many years that can use amount of radioisotope that are so tiny they are not harmful. Unfortunately the method is complicated and has been poorly described, so it is not used as much in human nutrition as it should be. We explain how to convert biological samples such as blood to a form that can be used for accelerator mass spectrometry. Our method will help other scientists learn how to use this powerful method.
Technical Abstract: Isotope tracer studies, particularly 14C measurements, are important tools in the biological, nutritional, and environmental sciences. Accelerator mass Spectrometry (AMS) is the most sensitive isotopic method but despite this advantage, AMS is not a routine laboratory method. A major reason why AMS use is rare is that sample preparation for AMS is difficult. Biological and environmental samples must be reduced to solid graphite before they can be analyzed by AMS. Dried organic samples are transferred into pre-baked quartz tubes, a small amount of copper oxide is added, and the tubes are heat-sealed under vacuum. The samples are then combusted at 900 oC for 2 h. The resulting CO2 is cryogenically transferred into septa sealed reaction vials containing iron and zinc catalysts under vacuum. The reaction vials are heated at 525oC for 6 h to form graphite, then the graphite produced is pounded into aluminum target holders. Improvements and mechanization of this multi-step procedure has been slowed, in part, because there are few organized training opportunities, manuals or how-to-it books for AMS sample preparation that would allow new investigators to work with the technique without a substantial outlay of time and effort. We diagram a detailed sample preparation protocol for graphitizing biological samples for AMS, and include examples of nutrition studies that have used this procedure.