Novel Injection Techniques to Enable Fast, High Peak Capacity Gas Chromatography Separations

Abstract

To achieve faster gas chromatographic (GC) analysis of increasingly complex samples requires improved peak capacity production (peak capacity per separation run time) from the separation. The increased peak capacity production was achieved by selecting appropriate experimental conditions based on theoretical modeling of on-column band broadening , by reducing the injection pulse width, and by the implementation of a second, serially connected column to make a GC × GC instrument. Modeling to estimate the on-column band broadening from experimental parameters provided insight to achieving GC separations in the absence of off-column band broadening (the additional band broadening not due to the on-column separation process). In order to optimize separations collected on a traditional GC platform, off-column band broadening from injection was significantly reduced by using a variety of modified injection devices (includeing diaphragm valves, commercially available thermal modulators, and a custom built high speed cryofocusing injector) to generate narrow pulses on the separation column for both isothermal and temperature programmed separations. Additionally, off-column band broadening from detection was minimized by implementation of fast detectors such as flame ionization detectors (FID) and time-of-fligh mass spectrometry (TOFMS) collecting data at rates greater than 500 Hz. This resulted in a 2 to 3-fold improvement in peak capacity production compared to standard GC practice. The optimized injection techniques and separation conditions described above were also applied to GC × GC instrumentation with both valve and thermal modulators, resulting in 5 to 10-fold improvement in peak capacity production relative to traditional instruments.