predictability of the elution order by the theory. In addition, Baycan-Keller and
Oehme presented calculation procedures that allow the prediction of the best possible isomer and enantiomer separation at the shortest possible tandem system. The
latter argument was assumed to be important, because enantiomer separation is
usually best at low temperatures. The procedure suggested by Baycan-Keller and
Oehme only requires the measurements of the retention times and of the column hold
up time of the single columns. The authors stress that for the determination of the
optimum length of the single columns for the tandem system, a substantial amount of
calculations is necessary. However, they are mathematically trivial and, thus, simple
computer programs can be used (Hühnerfuss and Shah 2009).
Additional examples for successful applications of tandem GC with regard to
enantiomer separation of chiral environmental pollutants can be found in publications by Garrison et al. (1997), who investigated the enantioselectivity, or lack of,
occurring during the environmental degradation and biological exposure of o,p-DDT
and -DDD investigated by tandem GC and M-CEKC (Sect. 4.1). With regard to
tandem GC, the combination of permethyl-trifluoroacetoxypropyl-γ-cyclodextrin
(Chiraldex G-PT) as chiral stationary phase and an achiral XTI-5 column (5%
diphenyl, 95% dimethyl polysiloxane phase), in that order, provided excellent
separation of the six main DDT isomers/congeners (o,p
0 -DDT, -DDD and -DDE,
and p,p
0 -DDT, -DDD and -DDE) as well as baseline separation of the enantiomers of
o,p
0 -DDT and, for the needs of their experiments, of o,p
0 -DDD. Reversal of order of
the columns provided little additional efficiency over that using the γ-cyclodextrin
column alone. Although the enantiomeric separation was approximately the same
with the chiral column alone as with the tandem columns, without the XTI-5 column,
one of the enantiomers of each of the two chiral compounds overlapped to the extent
that it was impossible to determine whether the loss of o,p
0 -DDT or the formation of
o,p
0 -DDD was enantioselective.
5.5 Recent Reviews on Enantioselective HRGC
Recent reviews and updated overviews that appeared in recent years on
enantioselective HRGC include several relevant publications worth mentioning
here (Schurig 2010, Schurig 2013, Schurig and Kreidler 2013, Badea et al. 2016,
Xie and Yuan 2017, Elbashir and Aboul-Enein 2018, Gumustas et al. 2018). These
reviews are mainly dealing with analytical separation techniques and application of
enantiomer-selective separation in environmental sciences, drug development and
medical sciences.
82
5 Enantiomer-Selective High-Resolution Gas Chromatography (esHRGC)
Oehme presented calculation procedures that allow the prediction of the best possible isomer and enantiomer separation at the shortest possible tandem system. The
latter argument was assumed to be important, because enantiomer separation is
usually best at low temperatures. The procedure suggested by Baycan-Keller and
Oehme only requires the measurements of the retention times and of the column hold
up time of the single columns. The authors stress that for the determination of the
optimum length of the single columns for the tandem system, a substantial amount of
calculations is necessary. However, they are mathematically trivial and, thus, simple
computer programs can be used (Hühnerfuss and Shah 2009).
Additional examples for successful applications of tandem GC with regard to
enantiomer separation of chiral environmental pollutants can be found in publications by Garrison et al. (1997), who investigated the enantioselectivity, or lack of,
occurring during the environmental degradation and biological exposure of o,p-DDT
and -DDD investigated by tandem GC and M-CEKC (Sect. 4.1). With regard to
tandem GC, the combination of permethyl-trifluoroacetoxypropyl-γ-cyclodextrin
(Chiraldex G-PT) as chiral stationary phase and an achiral XTI-5 column (5%
diphenyl, 95% dimethyl polysiloxane phase), in that order, provided excellent
separation of the six main DDT isomers/congeners (o,p
0 -DDT, -DDD and -DDE,
and p,p
0 -DDT, -DDD and -DDE) as well as baseline separation of the enantiomers of
o,p
0 -DDT and, for the needs of their experiments, of o,p
0 -DDD. Reversal of order of
the columns provided little additional efficiency over that using the γ-cyclodextrin
column alone. Although the enantiomeric separation was approximately the same
with the chiral column alone as with the tandem columns, without the XTI-5 column,
one of the enantiomers of each of the two chiral compounds overlapped to the extent
that it was impossible to determine whether the loss of o,p
0 -DDT or the formation of
o,p
0 -DDD was enantioselective.
5.5 Recent Reviews on Enantioselective HRGC
Recent reviews and updated overviews that appeared in recent years on
enantioselective HRGC include several relevant publications worth mentioning
here (Schurig 2010, Schurig 2013, Schurig and Kreidler 2013, Badea et al. 2016,
Xie and Yuan 2017, Elbashir and Aboul-Enein 2018, Gumustas et al. 2018). These
reviews are mainly dealing with analytical separation techniques and application of
enantiomer-selective separation in environmental sciences, drug development and
medical sciences.
82
5 Enantiomer-Selective High-Resolution Gas Chromatography (esHRGC)