Page 430 - Multidimensional Chromatography

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to the fingerprinting of gasoline and other flammable materials. The first chro-
matogram (Figure 15.10(a)) shows the GC-infrared chromatogram from the first
dimension. There are approximately 110 peaks, which are significantly overlapped.
Four heart-cuts (A–C) were taken. On the second chromatogram (Figure 15.10(b)),
the GC/MS analysis of heart-cut C is shown. Twelve overlapping peaks that were
initially trapped were resolved into over 30 separated peaks. The combination of
non-destructive IR detection following the first stage and MS detection following the
second stage presents especially powerful third and fourth dimensions, thus allowing
spectral confirmation of peak identities and identification of overlaps.
The fragrance compounds commonly used in cosmetics and household products
are some of the most common causes of contact dermatitis. These products often
contain complex matrix interferences such as emulsifiers, thickeners, stabilizers,
pigments, antioxidants and others, thus making the analytes of interest difficult to
analyze. Tomlinson and Wilkins have applied multidimensional GC, coupled to
infrared and mass spectrometry, to the analysis of common irritants from these com-
plex mixtures (24). These authors modified a commercially available GC–IR–MS
system to accommodate the second analytical column. By using an intermediate
polarity (Rtx-1701) initial column and a variety of second columns, they obtained
separations of a wide variety of fragrances. In order to evaluate the re-injection effi-
ciency of their system, they used a Grob test mixture (25). This was injected on to
the intermediate polarity column, and then the entire chromatogram was re-focused
into a trap and re-injected onto an Rtx-5 non-polar column. They estimated a re-
injection efficiency of about 85% between the two columns. The Grob test mixture
chromatograms are shown in Figure 15.11. The first chromatogram (Figure 15.11(a))
shows a Grob test mix separated on the first-dimension column. The entire chro-
matogram is cryogenically trapped and then re-injected onto the second column, to
give the chromatogram shown in Figure 15.11(b). This provides an excellent means
for assessing the efficiency of the interface between the two columns. Thorough
reviews of multispectral detection methods, such as GC–IR–MS, have been pro-
vided by Ragunathan et al. (26) and Krock et al. (27).
Authenticity evaluation has recently received increased attention in a number of
industries. The complex mixtures involved often require very high resolution analy-
ses and, in the case of determining the authenticity of ‘natural’ products, very accu-
rate determination of enantiomeric purity. Juchelka et al. have described a method
for the authenticity determination of natural products which uses a combination of
enantioselective multidimensional gas chromatography with isotope ratio mass spec-
trometry (28). In isotope ratio mass spectrometry, combustion analysis is combined
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with mass spectrometry, and the C/ C ratio of the analyte is measured versus a
CO 2 reference standard. A special interface, employing the necessary oxidation and
reduction reaction chambers and a water separator, was used employed. For stan-
dards of 5-nonanone, menthol and (R)- -decalactone, they were able to determine
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the correct C/ C ratios, with relatively little sample preparation. The technical
details of multidimensional GC–isotope ratio MS have been described fully by Nitz
et al. (29). A MDGC–IRMS separation of a natural cis-3-hexen-1-ol fraction is