Pressure-Tunable Dual-Column Ensembles for High-Speed GC and GC/MS

Abstract

SummaryA series-coupled ensemble of two capillary GC columns of different selectivity with an adjustable pressure at the column junction point is used to obtain tunable selectivity for high-speed GC and GC/ TOFMS. An electronic pressure controller with a 0.1-psi step size is used to obtain numerous computer-selected unique selectivities. System configurations for conventional, atmospheric-pressure outlet operation with flame ionization detection and for vacuum-outlet operation with photoionization detection are described for GC-only experiments. Polydimethylsiloxane is used as the non-polar column and polyethylene glycol (atmospheric outlet) or triflouropropylpolysiloxane (vacuum outlet) is used as the polar column. For GC/ TOFMS experiments, 5% phenyl polydimethylsiloxane was used as the non-polar column, and polyethylene glycol was used as the polar column. The time-of-flight mass spectrometer can acquire up to 500 complete mass spectra per second. Since spectral continuity is achieved across the entire chromatographic peak profile, severely overlapping peaks can be spectrally deconvoluted for high-speed characterization of completely unknown mixtures. For mixture components with significantly different fragmentation patterns, spectral deconvolution can be achieved for chromatographic peak separations of as little as 6.0 ms. This can result is very large peak capacity for time compressed (not completely resolved) chromatograms. The use of columns with tunable selectivity allows for precise peak-position control, which can result in more efficient utilization of available peak capacity and thus further time compression of chromatograms. The limits of tunability and deconvolution are tested for near co-elutions of different classes of hydrocarbon compounds as well as for more multi-functional mixtures.

A Portable, High-Speed, Vacuum-Outlet GC Vapor Analyzer Employing Air as Carrier Gas and Surface Acoustic Wave Detection

“…and use 0.25-μm-thick bonded stationary phases. An electronic pressure controller PC (with pneumatic restrictor R) can be used to control the carrier gas (air) pressure at the column junction point in order to tune the selectivity of the column ensemble for specified sets of target compounds. , This feature was not used in the present study, and the column ensemble was operated with a junction pressure set point equal to the pressure that would occur in the absence of any other external connections. These set-point pressure values were calculated for various ensemble outlet pressures from standard equations for gas flow in capillary tubes. , This procedure keeps the ratio of holdup times for the two columns nearly constant and is necessary so that the outlet pressure could be varied over a relatively wide range without large changes in ensemble selectivity.…”

GC models for separation optimization in pressure-tuneable tandem capillary columns operated isothermally. Part 1: Theoretical aspects

“…In the 70s, the diffusion of the first electronic devices for the dynamic control of gas flow and pressure made an innovative approach possible. Selectivity was tuned by adjusting carrier gas pressure at the junction of two capillary columns containing different stationary phases and connected in series . This new technique, called “selectivity tuning” or “tandem‐column chromatography,” made use of differential control of carrier gas velocity in the two capillary columns to produce a gradual change of residence times in each column.…”

Analysis of polychlorodibenzo‐p‐dioxins and polychlorodibenzofurans in stationary source emissions in GC–MS/MS using hydrogen as the carrier gas

“…The vacuum decreases by about one order of magnitude with H 2 (compared to He in the same chromatographic conditions) due to the less viscosity of the gas and the consequent less efficiency of the pumping system. Working with a smaller diameter column can be an alternative to use hydrogen without losing MS efficiency such as in the fast GC analysis .…”