Programmable Control of Column Selectivity for High-Speed GC

Abstract

A tandem-column ensemble consisting of two capillary columns with different stationary-phase chemistries and computer-controlled carrier-gas pressure at the column junction point is used to change the ensemble selectivity on-the-fly during a separation. When the pressure at the column junction point is changed, differential changes occur in the carrier gas velocities in the two columns. This changes the relative contribution that each column makes to the ensemble selectivity. This programmable selectivity control is applied to the problem of high-speed, isothermal GC analysis of volatile organic compound (VOC) mixtures. For the ensemble configuration described here, the pressure control system provides over 200 computer-selected junction-point pressures in 0.1 psi steps. Repeatability typically is ±0.01 psi. This provides for very stable retention patterns. The relatively large dead volume in the controller is managed by the use of a pneumatic vent line. The vent line restriction is set to give pressure set-point transition times of 0.3−3 s. A model is developed to aid in the selection of the pressure program (pressure vs time profile) that will result in a rapid separation of the target compounds. The model results in plots of the position of component bands in the column ensemble vs time. These sample-band trajectory plots show discontinuous changes in slope (migration velocity) at pressure set-point change times and when each component band migrates across the column junction. The model provides quantitative information on elution peak positions. The model is used to predict the effects of changes in the selectivity program on retention patterns.

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.…”

Chromatographic separation of simulants of nerve and blister agents by combining one‐ and two‐channel columns with different stationary phases

“…Nevertheless, the introduction of modulator also increases the complexity of the chromatographic system . On the other hand, Grall and Leonard confirmed that an optimal combination of different stationary phases, in traditional capillary columns, provide an elevated resolution for the separation of compounds in complex mixtures. However, there has been little work tracking the separation of the simulants of nerve and blister agents by using a combination of two microfabricated columns with different stationary phases.…”

A multidimensional micro gas chromatograph employing a parallel separation multi-column chip and stop-flow μGC × μGCs configuration

“…The dual-column tunable separation was first established and extensively studied by Sacks and co-workers. 28 The idea was to take advantage of the different retention behaviors of two stationary phases in series and to modulate the elution time for certain co-eluting peaks in order to separate them. The elution behaviors of the mixtures in two columns of different stationary phases can be manipulated via either temperature programming 29 on each of the columns or by pressure modulation 30 at the junction point of dual columns.…”