Dramatic selectivity changes on carrier gas flow change in a series‐coupled GC capillary tandem

Abstract

We describe the polarity of selectivity of a GC separation system in terms of Retention Index data. In a series-coupled capillary system having stationary phases of differing polarity even slight (independent!) carrier gas flow changes in one part of the capillary series result in a dramatic change of selectivity. "Dramatic" is a relative term! Using a simple electronically controlled flow changing device we found retention index changes of several hundred units for polar test compounds such as phenols on a SESOKarbowax tandem. This means: The classical theoretical model for understanding retention (and selectivity) in chromatography must be corrected. We propose a very simple approach involving addition of the expression RESIDENCE TIME to the chromatographic vocabulary. Instead of using flow resistors, one can just add a pressure regulator to the coupling point. A powerful analytical concept is now in easy reach.

GC models for separation optimization in pressure‐tunable tandem capillary columns operated isothermally

“…Its seals may also release unwanted substances when they are lapped by the carrier gas before entering the second column. Several authors have attempted to solve the problem by proposing thimble‐, double‐T‐ or cross‐shaped connection systems. Nevertheless, their use has been hampered by a number of difficulties in obtaining a correct and reproducible alignment of the two columns.…”

Fundamental Relationships of Chromatography

“…The residence time of the sample in the two columns can be adjusted by changing the relative column lengths, by adjusting the average linear velocity of the carrier gas in the two columns to preselected values, or by operating the columns at different temperatures in a dual oven gas Chromatograph [174][175][176][177][178]. For practical convenience, the junction between the two columns is both pressure and flow controlled with also, for convenience of accurately setting the experimental conditions for the first column, the possibility of diverting a fraction of the sample from the first column to a detector.…”

“…Thus, unless the mixture is very complex or contains components that are particularly difficult to separate it may be possible to optimize a particular separation using the linear equation (1.72) as demonstrated by Ettre [177]. Thus, unless the mixture is very complex or contains components that are particularly difficult to separate it may be possible to optimize a particular separation using the linear equation (1.72) as demonstrated by Ettre [177].…”

Progress in all‐glass stream splitting systems in capillary gas chromatography. Part I: Application of a simple “glass‐cap‐cross” as effluent splitter for splitless and on‐column injection

“…The tandemcapillariesinsucha MGCsystemareconnected by theaid ofaso-called "IFC-cross", acompletely deadvolume freecapillary connecting device (see Figure 2 in ref. [19] and Figure 3 in ref.…”