Page 27 - 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)

2 Coupled High Performance Liquid
Chromatography with High

Resolution Gas Chromatography

L. MONDELLO
Università di Messina, Messina, Italy

2.1 INTRODUCTION
The analysis of complex matrices, such as natural products, food products, environ-
mental pollutants and fossil fuels, is today a very important area of separation sci-
ence. The latest developments in chromatographic techniques have yielded highly
efficient systems, used with specific detectors to obtain high selectivity and or sensi-
tivity.
Sometimes, the resolving power attainable with a single chromatographic system
is still insufficient for the analysis of complex matrices. An approach commonly
used to obtain greater resolution is multidimensional chromatography.
In the specific case of high performance liquid chromatography coupled with
high resolution gas chromatography (HPLC–HRGC), the selectivity of the LC sepa-
ration is combined with the high efficiency and sensitivity of GC separation, thus
giving a relatively high peak capacity. Off-line coupling of LC and GC is frequently
used because of the ease of collecting and handling liquids, but this technique is long
and laborious, and involves numerous steps with the risk of contamination, forma-
tion of artifacts and possible loss of sample. On-line coupling of LC and GC presents
a number of advantages: the amount of sample required is less, there is no sample
work-up, no evaporation or dilution is necessary, and fully automated sample pre- or
post-treatments are possible. The disadvantages of the on-line system are that the
system is more difficult to operate, the initial set-up is expensive, and interfaces are
relatively complicated. The main problem to be solved in on-line LC–GC coupling is
the transfer of amounts of liquid from LC to GC, where the latter operates in a differ-
ent physical state. Different approaches have been studied for allowing the introduc-
tion of large amount of solvent into the GC column. These techniques must
selectively remove the solvent, thus leaving the solute in a sharp band at the entrance
to the separation column.