Page 405 - Multidimensional Chromatography

Multidimensional Chromatographic Applications in the Oil Industry 397

Figure 14.18 Typical GC chromatogram of the separated mono-aromatics fraction of a mid-
dle distillate sample; the numbers indicate the retention time of the various n-alkanes.

The system described in the previous section has been extended with a sulfur
chemiluminescence detector (SCD) for the detection of sulfur compounds (32). The
separated fractions were thiols sulfides thiophenes (as one group), benzothio-
phenes, dibenzothiophenes and benzonaphtho-thiophenes. These four groups have
been subsequently injected on-line into and separated by the GC unit. Again, no
overlap between these groups has been detected, as can be seen from Figure 14.20,
in which the total sulfur compounds are shown and from Figure 14.21 in which the
separated dibenzothiophenes fraction is presented. The lower limit of detection of
1
this method proved to be 1 ppm (mg kg ) sulfur per compound.

14.4.4 COMPREHENSIVE TWO-DIMENSIONAL GAS
CHROMATOGRAPHY (GC
GC)

When John Phillips, in 1991, presented the practical possibility of acquiring a real
comprehensive two-dimensional gas chromatographic separation (33), the analytical
chemists in the oil industry were quick to pounce upon this technique. Venkatramani
and Phillips (34) subsequently indicated that GC
GC is a very powerful technique,
which offers a very high peak capacity, and is therefore eminently suitable for
analysing complex oil samples. These authors were able to count over 10 000 peaks
in a GC
GC chromatogram of a kerosine. Blomberg, Beens and co-workers