Application of a flow-tunable, serially coupled gas chromatographic capillary column system for the analysis of complex mixtures

Abstract

SummaryA capillary column gas chromatographic system employing two serially coupled fused-silica columns and a simple coupling element is described. The system is operated in flow-tunable mode (flow-tunable tandem system). The very fact of continuous tuning over a large polarity (selectivity) range, ultimately determined by the two constituent columns, offers several possibilities in the analysis of complex mixtures. In this paper two applications are discussed in detail: optimization of peak separation and peak identification. For these applications it is feasible to use, retention data collected from experiments on the tandem system, and empirical formulas. A relatively simple theoretical mathematical model valid for the flow-tunable tandem system, however, furnishes an easy way of calculating retention data on the system from data collected from the individual single columns, thus, creating a new possibility for optimization and peak identification. Optimization and peak identification processes using the empirical and theoretical models are both demonstrated by analysis of solvent mixtures.

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

“…In order to clear this hurdle, we have developed a different approach based on the combined use of thermodynamic relationships between distribution constants and temperature and the mathematical equations developed by Deans and Scott , Hinshaw Jr. and Ettre , and Garay . Although the proposed approach is applicable, in principle, to a series of two columns also kept at different temperatures, it has exclusively been applied to assemblies operating at a common isothermal temperature as they represent the configuration more easily implementable in current commercial gas chromatographs.…”

“…As from 1973, a few eminent researchers showed how the theoretical description of a tandem‐column assembly may be obtained by combining fundamental relationships on GC with very few basic equations valid for multichromatographic systems. Their mathematical analysis was applied to tandem‐column systems made up of two chromatographic columns that can differ from each other for the polarity of the stationary phase and, if necessary, for their geometric characteristics.…”

“…Not more than a dozen phases were used to meet most of practical needs. In recent years the development of fast GC with short columns as well as the need to separate complex mixtures containing more than a hundred compounds have relaunched the interest in selectivity optimization .…”

“…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.…”

Serial versus parallel columns using isocratic elution: A comparison of multi-column approaches in mono-dimensional liquid chromatography

“…The idea of serially coupling stationary phases (Fig. 1a) to analyse complex samples appeared early in the development of chromatography [4,18,19]. However, this approach has been only feasible when the connection between columns has been improved to avoid the undesirable presence of void volumes and changes in the packing material close to the junctions.…”