An Interface for Direct Analysis of 14C in Nonvolatile Samples by Accelerator Mass Spectrometry

We describe here apparatus and methods for direct analysis of 14C in biological specimens by accelerator mass spectrometry (AMS). Liquid samples, including plasma and urine, are deposited by pipet into a bed of CuO powder that fills a space within a rigid, refractory support. Volatile components are removed under reduced pressure prior to analysis. The CuO matrix is locally heated with an infrared laser while it is contained within a sealed chamber that is swept with He carrier gas. Heating induces combustion of the applied sample, and the carrier gas transports the CO2 that is formed to the AMS instrument's ion source, which is appropriately modified for use with CO2. A rodent study of drug clearance with [14C]-acetaminophen was performed to provide plasma and urine specimens, which were analyzed with this overall approach and by liquid scintillation counting for comparison. Results presented here confirm the potential utility of laser-induced sample combustion as an alternative to graphite production for AMS analysis of 14C. Anticipated benefits of the present approach include reduced risk of sample cross-contamination, decreased analysis time, and greater compatibility with robotics.