Tunable-Column Selectivity and Time-of-Flight Detection for High-Speed GC/MS

A pressure-tunable ensemble of two capillary separation columns is combined with time-of-flight mass spectral detection for the high-speed characterization and analysis of volatile organic compounds. The detector can record up to 500 complete mass spectra per second and can obtain spectral deconvolution and thus characterization of severely overlapping and unknown chromatographic peaks. The tunable capillary column ensemble consists of the series combination of a nonpolar 5% phenyl poly(dimethylsiloxane) column and a polar poly(ethylene glycol) column. Adjustment of the pressure at the column junction point is achieved by the use of an electronic pressure controller. Changes in the junction pressure result in changes in the relative contribution that each of the columns makes to overall retention. This causes changes in the retention patterns, which can be used to enhance the utility of the TOFMS detector. The use of high spectral acquisition rates allows for the deconvolution of very closely spaced peaks. Adjustment of the column junction pressure often allows for the control of peak separation for critical component pairs. Since severely overlapping chromatographic peaks can be tolerated in many cases, the time axis of the chromatogram can be compressed, thus obtaining very fast GC/MS characterization of unknown mixtures. Tunable columns are very useful for facilitating time compression since significant control of relative peak positions can be achieved.