PREPARATION METHODS OF μg CARBON SAMPLES FOR 14C MEASUREMENTS

Systematic investigations and experience from several application projects on small carbon samples over a number of years have resulted in measuring the radiocarbon content of 10 mu g C samples with an overall precision of typically 1%. A substantial reduction of the carbon contamination during graphitization was achieved, resulting in 31 +/- 30 ng modern and <100 ng C-14-free carbon. Thus, graphitization is no longer the limiting factor because earlier sample preparation steps usually introduce much larger contamination. The method has been extended to a variety of materials and applied to various projects. Realistic conditions for procedure development can only be achieved in the context of applications on true samples; methods developed are the lyophilization of samples in solution, combustion, ultraviolet oxidation, or carbonate hydrolysis with phosphoric acid, which allows to prepare samples for a wide range of applications. Insights gained from systematic investigations and from real applications are presented.