On-line pyrolysis as a limitless reduction source for high-precision isotopic analysis of organic-derived hydrogen

On-line pyrolysis is described as an alternative to chemical means for reducing organic compounds to hydrogen gas for hydrogen isotopic analysis by continuous-flow isotope ratio mass spectrometry. An empty ceramic tube, held at temperatures above 1000 degree C, is used in-line to pyrolyze organic compounds separated by gas chromatography and is followed by a hydrogen-selective filter and isotope ratio mass spectrometer for hydrogen purification and isotopic measurement. Precision of light gas D/H isotopic measurement over several-fold signal intensity is shown to average SD < 2% (delta D), with corrections for ion source nonlinearities. It is demonstrated that isotopic measurement using pyrolysis is indefinitely stable, as opposed to the gradual loss of isotopic accuracy using on-line chemical reactors due to degradation of the reducing capacity of reactor metals. Pyrolytic conversion to hydrogen becomes more efficient with increasing temperature, although quantitative conversion was not achieved at the highest temperature tested (1150 degree C) in our system. In addition, pyrolysis efficiency varies with compound type; therefore, the technique requires a separate calibration for each compound of interest. This approach shows promise as a component of a robust and low-maintenance system.