validation methods (see above). The enantiomeric signature is, however, determined
by the retention difference of the enantiomers during chromatographic separation.
Thus, ideally, the absolute structure, but at least the polarographic properties (discrimination of (+)- and (À) enantiomers) must be established and associated with the
eluting target peak in the chromatogram (Ermer and Vogel 2000; Nageswara Rao et al.
2006; He et al. 2015). The confirmation of the elution order needs to be performed
with well-characterised enantiomer enriched/enantiomeric pure standard solutions
whenever an enantiomer-selective chromatographic column is changed (even in case
of similar CSPs). For many CSPs, the enantioselective separation mode is not
completely elucidated. Thus, batch-to-batch differences where chiral impurities
(known or unknown), introduced during the production processes, may contribute
significantly to the elution order of the target enantiomers (Szepesi and Gazdag 1988;
Jaus and Oehme 2001; Berthod 2010; Dousa et al. 2016) need to be considered.
7.1 Enantiomer Distribution in Environmental Samples
Generally, the enantiomer distribution of anthropogenic pollution today is considered as an indicator of bioavailability and, thus, illustrates the toxic potential in
environmental risk assessment. It is simply assumed that chiral anthropogenic
pollutants are introduced into the environment as racemates and that significant
deviations from the racemic distribution indicate bioavailability and biotransformation (Ali and Aboul-Enein 2004). However, the synthesis and production of a
selected number of chiral agents is based on enantiomeric pure natural compounds.
As an example, the Toxaphene
® mixture, containing several hundred
chlorobornanes, chlorobornenes and chlorobornadienes, is produced in the USA
using excessive chlorination of camphene (2,2-dimethyl-3-methylidenebicyclo
[2.2.1]heptane). Toxaphene
® was used as a pesticide mixture in cotton and soybean
production in the period 1960–1980 but is now globally banned as agricultural aid.
Camphene is the starting material for the Toxaphene
® product, but also for many
other substances as well, among other fragrances and food additives. However,
camphene is, in turn, synthesised by catalytic isomerisation of the naturally occurring α-Pinene. In North America the 1R,5R-(+)-α-Pinene is usually present in pine
trees, whereas the 1S,5S-(À)-α-Pinene is common in European pine trees (Miller
et al. 2003; Chiu et al. 2017). Thus, non-racemic starting material must be assumed
(although not confirmed by the producer). Nikiforov and coworkers simulated the
synthetic pathway of Polychloropinene
® , the product name for a similar
chlorobornane/chlorobornadiene/chlorobornene mixture as Toxaphene
® , used
extensively as a pesticide in the former USSR. As starting material pure 1S,5S(À)-α-Pinene for excessive chlorination was used and non-racemic distribution of
indicator compounds in the resulting technical mixtures was found (Trukhin et al.
2007). Three indicator compounds were isolated and the X-ray crystallography
confirmed enantiomeric pure compounds (one example, Fig. 7.1.).
Today, pharmaceutical and personal care products (PPCPs) are an important
focus as environmental residues in aqueous environments. Caused by public
98
7 Quality Control and Evaluation Criteria for Enantiomer-Selective Separation. . .
by the retention difference of the enantiomers during chromatographic separation.
Thus, ideally, the absolute structure, but at least the polarographic properties (discrimination of (+)- and (À) enantiomers) must be established and associated with the
eluting target peak in the chromatogram (Ermer and Vogel 2000; Nageswara Rao et al.
2006; He et al. 2015). The confirmation of the elution order needs to be performed
with well-characterised enantiomer enriched/enantiomeric pure standard solutions
whenever an enantiomer-selective chromatographic column is changed (even in case
of similar CSPs). For many CSPs, the enantioselective separation mode is not
completely elucidated. Thus, batch-to-batch differences where chiral impurities
(known or unknown), introduced during the production processes, may contribute
significantly to the elution order of the target enantiomers (Szepesi and Gazdag 1988;
Jaus and Oehme 2001; Berthod 2010; Dousa et al. 2016) need to be considered.
7.1 Enantiomer Distribution in Environmental Samples
Generally, the enantiomer distribution of anthropogenic pollution today is considered as an indicator of bioavailability and, thus, illustrates the toxic potential in
environmental risk assessment. It is simply assumed that chiral anthropogenic
pollutants are introduced into the environment as racemates and that significant
deviations from the racemic distribution indicate bioavailability and biotransformation (Ali and Aboul-Enein 2004). However, the synthesis and production of a
selected number of chiral agents is based on enantiomeric pure natural compounds.
As an example, the Toxaphene
® mixture, containing several hundred
chlorobornanes, chlorobornenes and chlorobornadienes, is produced in the USA
using excessive chlorination of camphene (2,2-dimethyl-3-methylidenebicyclo
[2.2.1]heptane). Toxaphene
® was used as a pesticide mixture in cotton and soybean
production in the period 1960–1980 but is now globally banned as agricultural aid.
Camphene is the starting material for the Toxaphene
® product, but also for many
other substances as well, among other fragrances and food additives. However,
camphene is, in turn, synthesised by catalytic isomerisation of the naturally occurring α-Pinene. In North America the 1R,5R-(+)-α-Pinene is usually present in pine
trees, whereas the 1S,5S-(À)-α-Pinene is common in European pine trees (Miller
et al. 2003; Chiu et al. 2017). Thus, non-racemic starting material must be assumed
(although not confirmed by the producer). Nikiforov and coworkers simulated the
synthetic pathway of Polychloropinene
® , the product name for a similar
chlorobornane/chlorobornadiene/chlorobornene mixture as Toxaphene
® , used
extensively as a pesticide in the former USSR. As starting material pure 1S,5S(À)-α-Pinene for excessive chlorination was used and non-racemic distribution of
indicator compounds in the resulting technical mixtures was found (Trukhin et al.
2007). Three indicator compounds were isolated and the X-ray crystallography
confirmed enantiomeric pure compounds (one example, Fig. 7.1.).
Today, pharmaceutical and personal care products (PPCPs) are an important
focus as environmental residues in aqueous environments. Caused by public
98
7 Quality Control and Evaluation Criteria for Enantiomer-Selective Separation. . .