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Figure 15.2 Three-stage LC–GC–GC separation of stilbenes from corned beef: (a) initial
HPLC stage; (b) first GC stage; (c) second GC stage showing separated analytes. Peak identi-
fication in (c) is as follows: a, trans-diethylstilbesterol; b, cis-diethylstilberterol; c, hexestrol;
d, dienestrol. Adapted from Journal of High Resolution Chromatography, 16, G.C. Chappell
et al., ‘On line high performance liquid chromatography–multidimensional gas chromatogra-
phy and its application to the determination of stilbene hormones in corned beef, pp.
479–482, 1993, with permission from Wiley-VCH.

LC–GC, therefore, shows promise for forensic science applications, reducing
sample handling and preparation steps by essentially using an on-line LC column in
place of one or more extraction steps. This is followed by a traditional high resolu-
tion GC analysis. The methods described here for pesticides and hormones could be
readily adapted to a variety of analyses, especially those involving fatty matrices,
such as tissues, food or blood.

15.3 LIQUID – CHROMATOGRAPHY–LIQUID CHROMATOGRAPHY

Multidimensional liquid chromatography (LC–LC) has been employed mainly in
efforts to directly inject biological materials such as urine, blood, plasma or serum,
without prior clean-up steps. The particular advantage of direct injection methods
actually lies in the disadvantages of classical extraction and preparation methods,
which require extensive handling of potentially infectious samples, and losses of
material due to these handling steps. Multidimensional chromatography also lends
itself well to automation, which may be required in forensic or drug-monitoring lab-
oratories. The analytes of interest in the direct injection of biological fluids include
mostly drugs and other compounds of clinical interest. The use of guard columns and
other pre-column devices is not described here, as these are generally used only for
sample clean-up, rather than for improvement of fundamental chromatographic per-
formance. Most systems for multidimensional LC–LC consist of two or more
columns connected by column switching pneumatics, and these are described in
detail in Chapter 5 of this text. Several examples of drug analysis from blood and