TARGET PREPARATION FOR CONTINUOUS-FLOW ACCELERATOR MASS-SPECTROMETRY

For very small samples, it is difficult to prepare graphitic targets t hat will yield a useful and steady sputtered ion beam. Working with ma terials separated by preparative capillary gas chromatography, we have succeeded with amounts as small as 20 mu g C. This seems to be a prac tical limit, as it involves 1) multiple chromatographic runs with trap ping of effluent fractions, 2) recovery and combustion of the fraction s, 3) graphitization and 4) compression of the resultant graphite/coba lt matrix into a good sputter target. Through such slow and intricate work, radiocarbon ages of lignin derivatives and hydrocarbons from coa stal sediments have been determined. If this could be accomplished as an ''online'' measurement by flowing the analytes directly into a micr owave gas ion source, with a carrier gas, then the number of processin g steps could be minimized. Such a system would be useful not just for chromatographic effluents, but for any gaseous material, such as CO2 produced from carbonates. We describe tests using such an ion source.