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, r esolution, and maintenance of a continuous-now gas isotope ratio syste m. Chromatographic peak shapes were preserved by minimizing changes in tubing diameter and dead volumes. A single piece of fused silica capi llary was used to connect the gas chromatograph (GC) to the isotope ra tio mass spectrometer (IRMS), thus eliminating extraneous combustion f urnace and water trap fittings. Analysis of a standard mixture of hydr ocarbons yielded a 2-fold increase in signal over a slightly modified conventional system. Column efficiency, expressed as trennzahl (TZ), i mproved significantly (Student's t-test 95% CI) by an average factor o f 1.4 for replicates analyzed under similar conditions. The design is robust, requires less maintenance, and reduces leaks because the numbe r of connections is minimized. Benefits of this system are transferabl e to virtually all commercially available continuous-now systems.