New trial methods for the detection of carbon and nitrogen in quartz samples

Common metamorphic quartz samples have abundant fluid inclusions that contain C, N, H2O, etc. Understanding the nitrogen content in quartz is especially important since neutron capture by nitrogen would contribute a significant amount of the total in situ14C production in exposed quartz by cosmic rays. To determine the carbon and nitrogen content experimentally, we applied nuclear reaction analysis (NRA) using a deuteron beam. The nuclear reactions of 14N(d, α0) and 12C(d, p0) were used to estimate atomic concentrations of N and C, respectively. In our six samples, the range of nitrogen concentration was 0.008 ± 0.001 to 0.050 ± 0.002 at%, and the carbon content ranged from 0.0005 ± 0.0003 to 0.0017 ± 0.0003 at%. The large errors associated with these estimates are due to low counting statistics from measurements of trace concentrations near the limits of detection. A Costech Elemental Analyzer was also used to determine nitrogen and carbon content. The nitrogen content of the quartz varied from 0.001 to 0.002 wt%, consistent with the NRA measurements, but with poor precision because the concentrations are close to the limit of detection. The carbon concentrations of our samples ranged from 0.0086 to 0.0242 wt% with better-defined chromatogram peaks than those of nitrogen. Further investigation is needed for the development of a reliable method of determination of C and N in quartz samples that could be used for in situ14C analysis for exposure dating applications [D. Lal, A.J.T. Jull, Nucl. Instr. and Meth. B 92 (1994) 291].