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408 Multidimensional Chromatography

forensic science as in environmental and food science, many of the methods and
ideas presented in those areas could be readily applied to forensic problems. Little
detail in instrumental set-ups is given here, as these are described elsewhere in this
volume.

15.2 LIQUID CHROMATOGRAPHY– GAS CHROMATOGRAPHY

Liquid chromatography (LC) has been used primarily as an on-line sample clean-up
method prior to high resolution capillary GC analysis. Primarily, this has involved
the retention of fats and other high-molecular-weight matrix components in the anal-
ysis of drugs or pesticides from a variety of matrices such as foods, tissues and fat.
LC–gas chromatography (GC) has not been widely employed in forensic and toxi-
cological analysis, although this technique shows promise for simplifying sample
preparation, especially in cases where sample volume is limited.
Van der Hoff, and co-workers (4–6) have used on-line LC–GC to separate and
determine organochlorine pesticides and polychlorinated biphenyls (PCBs) from a
variety of fatty matrices, including cow’s and human milk, and liposuction biopts. In
the most recent method, following treatment with sodium oxalate and extraction
with hexane, these authors used a normal phase HPLC column, (typically, 50 mm
1 mm 3 m Hypersil 50, or 30 mm 2.1 mm 5 m Spherisorb) followed by
direct transfer to capillary GC with electron-chapture detector (ECD) detection.
They found detection limits of about 0.3–2 g/kg of fat for a variety of pesticides
and PCB’s from milk. This paper provides an excellent example of how LC–GC
could be employed for the analysis of many other compounds of toxicological inter-
est from fatty matrices. Barcarolo (7) also provides an LC–GC method for pesticide
residues from fat, using a reversed phase clean-up prior to high resolution capillary
GC. A description of a home-built LC–GC system is provided, along with extensive
experimental detail. An LC–GC–ECD chromatogram of a butter sample, which
may be considered representative of other high-fat-content matrices is shown in
Figure 15.1. Several pesticides are successfully extracted from the fat matrix and
separated with a minimum of prior sample preparation. They also observed a limited
lifetime for the C 18 LC column of about 25–30 injections before washing was
required.
Chappell et al. (8) used LC coupled to two-dimensional GC in the analysis of ille-
gal growth hormones from corned beef. In order to re-focus the chromatographic
bands between stages, cryogenic focusing was employed. Figure 15.2 shows the
three stages of separation of stilbene hormones form corned beef. The HPLC separa-
tion is shown in stage 1, in which a small sample is heart-cut into the first GC col-
umn. During the first GC separation, another sample is heart-cut into the second GC
column. The third chromatogram shows the complete separation of several hor-
mones, with a total analysis time of about 40 min. Chappell and co-workers also
show examples of the removal of matrix interferences by cryogenically focusing
them between the two GC columns.