Hardware modifications to an isotope ratio mass spectrometer continuous-flow interface yielding improved signal, resolution, and maintenance.

A home-built combustion interface was constructed to improve signal, resolution, and maintenance of a continuous-flow gas isotope ratio system. Chromatographic peak shapes were preserved by minimizing changes in tubing diameter and dead volumes. A single piece of fused silica capillary was used to connect the gas chromatograph (GC) to the isotope ratio mass spectrometer (IRMS), thus eliminating extraneous combustion furnace and water trap fittings. Analysis of a standard mixture of hydrocarbons yielded a 2-fold increase in signal over a slightly modified conventional system. Column efficiency, expressed as trennzahl (TZ), improved significantly (Student's t-test 95% CI) by an average factor of 1.4 for replicates analyzed under similar conditions. The design is robust, requires less maintenance, and reduces leaks because the number of connections is minimized. Benefits of this system are transferable to virtually all commercially available continuous-flow systems.