Achieving high peak capacity production for gas chromatography and comprehensive two-dimensional gas chromatography by minimizing off-column peak broadening

Abstract

By taking into consideration band broadening theory and using those results to select experimental conditions, and also by reducing the injection pulse width, peak capacity production (i.e., peak capacity per separation time) is substantially improved for one dimensional (1D-GC) and comprehensive two dimensional (GC × GC) gas chromatography. A theoretical framework for determining the optimal linear gas velocity (the linear gas velocity producing the minimum H), from experimental parameters provides an in-depth understanding of the potential for GC separations in the absence of extra-column band broadening. The extra-column band broadening is referred to herein as off-column band broadening since it is additional band broadening not due to the on-column separation processes. The theory provides the basis to experimentally evaluate and improve temperature programmed 1D-GC separations, but in order to do so with a commercial 1D-GC instrument platform, off-column band broadening from injection and detection needed to be significantly reduced. Specifically for injection, a resistively heated transfer line is coupled to a high-speed diaphragm valve to provide a suitable injection pulse width (referred to herein as modified injection). Additionally, flame ionization detection (FID) was modified to provide a data collection rate of 5 kHz. The use of long, relatively narrow open tubular capillary columns and a 40 °C/min programming rate were explored for 1D-GC, specifically a 40 m, 180 μm i.d. capillary column operated at or above the optimal average linear gas velocity. Injection using standard auto-injection with a 1:400 split resulted in an average peak width of ∼1.5 s, hence a peak capacity production of 40 peaks/min. In contrast, use of modified injection produced ∼500 ms peak widths for 1D-GC, i.e., a peak capacity production of 120 peaks/min (a 3-fold improvement over standard auto-injection). Implementation of modified injection resulted in retention time, peak width, peak height, and peak area average RSD%’s of 0.006, 0.8, 3.4, and 4.0%, respectively. Modified injection onto the first column of a GC × GC coupled with another high-speed valve injection onto the second column produced an instrument with high peak capacity production (500–800 peaks/min), ∼5-fold to 8-fold higher than typically reported for GC × GC.