Page 56 - Multidimensional Chromatography

Multidimensional Chromatography
Edited by Luigi Mondello, Alastair C. Lewis and Keith D. Bartle
Copyright © 2002 John Wiley & Sons Ltd
ISBNs: 0-471-98869-3 (Hardback); 0-470-84577-5 (Electronic)

3 Multidimensional High Resolution
Gas Chromatography

A. C. LEWIS
University of Leeds, Leeds, UK

3.1 INTRODUCTION

The coupling of gas chromatography columns to enable multidimensional separa-
tions has been widely reported in many areas of industrial and environmental analy-
sis. The application of multidimensional GC has been focused in essentially two
areas: (i) increasing peak capacity of the separation system, and (ii) increasing the
speed of analysis of the separation system. It was perhaps the former of these two
that drove the early interest in two-dimensional GC couplings, and this still remains
important today. Despite GC still being very much a developing technique, two-
dimensional systems, were being applied to the analysis of crude oil and refinery
products as early as the late 1960s (1). These early applications focused on achieving
a higher degree of deconvolution with a two-column system for the characterization
of feedstock and refinery fuels, and this over the past three decades has become a
recurring application of two-dimensional gas chromatography.
In common with all multidimensional separations, two-dimensional GC has a
requirement that target analytes are subjected to two or more mutually independent
separation steps and that the components remain separated until completion of the
overall procedure. Essentially, the effluent from a primary column is reanalysed by a
second column of differing stationary phase selectivity. Since often enhancing the
peak capacity of the analytical system is the main goal of the coupling, it is the rela-
tionship between the peak capacities of the individual dimensions that is crucial.
Giddings (2) outlined the concepts of peak capacity product and it is this function
that results in such powerful two-dimensional GC separations.
This present chapter will not focus on the statistical theory of overlapping peaks
and the deconvolution of complex mixtures, as this is treated in more detail in
Chapter 1. It is worth remembering, however, that of all the separation techniques, it
is gas chromatography which is generally applied to the analysis of the most com-
plex mixtures that are encountered. Individual columns in gas chromatography can,
of course, have extremely high individual peak capacities, for example, over 1000
6
with a 10 theoretical plates column (3), but even when columns such as these are