Page 14 - 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)

1 Introduction

K.D. BARTLE
University of Leeds, Leeds, UK

1.1 PREAMBLE

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The natural world is one of complex mixtures: petroleum may contain 10 –10 6
components, while it has been estimated that there are at least 150 000 different pro-
teins in the human body. The separation methods necessary to cope with complexity
of this kind are based on chromatography and electrophoresis, and it could be said
that separation has been the science of the 20th century (1, 2). Indeed, separation
science spans the century almost exactly. In the early 1900s, organic and natural
product chemistry was dominated by synthesis and by structure determination by
degradation, chemical reactions and elemental analysis; distillation, liquid extrac-
tion, and especially crystallization were the separation methods available to organic
chemists.
Indeed, great emphasis was placed on the presentation of compounds in crys-
talline form; for many years, early chromatographic procedures for the separation of
natural substances were criticized because the products were not crystalline. None
the less, the invention by Tswett (3) of chromatographic separation by continuous
adsorption/desorption on open columns as applied to plant extracts was taken up by
a number of natural product researchers in the 1930s, notably by Karrer (4) and by
Swab and Jockers (5). An early example (6) of hyphenation was the use of fluores-
cence spectroscopy to identify benzo[a]pyrene separated from shale oil by adsorp-
tion chromatography on alumina.
The great leap forward for chromatography was the seminal work of Martin and
Synge (7) who in 1941 replaced countercurrent liquid–liquid extraction by partition
chromatography for the analysis of amino acids from wool. Martin also realized that
the mobile phase could be a gas rather than a liquid, and with James first developed (8)
gas chromatography (GC) in 1951, following the gas-phase adsorption–chromato-
graphic separations of Phillips (9).
Early partition chromatography was carried out on packed columns, but in 1958
Golay, in a piece of brilliant inductive reasoning (10), showed how a tortuous path
through a packed bed could be replaced by a much straighter path through a narrow
open tube. Long, and hence highly efficient columns for GC, could thus be
fabricated from metal or glass capillaries, and remarkable separations were soon