6
ISSARASERIRUK ET AL.
2. Xie SM, Yuan LM. Recent progress of chiral stationary phases for
separation of enantiomers in gas chromatography. J Sep Sci.
2017;40(1):124‐137.
Plots of ln α as a function of 1/T and ln k′2 for analytes
with the three largest −ΔΔH values (o2, o3, and o4) are
illustrated in Figures 7 and 8, respectively. As shown in
Figure 7, enantioselectivities for the three analytes at the
same separation temperature were in the order of
3. König WA. Gas chromatographic enantiomer separation with
modified cyclodextrins. Heidelberg: Hüthig; 1992 168 p.
o3
>
o4
>
o2, similar to their −ΔΔH values.
4. Schurig V. Separation of enantiomers by gas chromatography.
J Chromatogr A. 2001;906(1‐2):275‐299.
Enantioselectivities for the analytes having the same
retention value follow a different order: Enantioselectivity
is the highest for amine o2, followed by o3 and o4, respec-
tively (Figure 8). Temperature had a lesser effect on reten-
tion for o2 as reflected by the lowest −ΔH and −ΔS values
(Figure 2), but a higher effect on the enantioselectivity.
Separation of three racemates with baseline resolution
and their analysis times are illustrated in Figure 9.
5. Španik I, Krupčik J, Skačáni I, Sandra P, Armstrong DW. On the
capillary gas chromatographic separation of enantiomers of
N‐trifluoroacetyl‐O‐alkyl esters of selected amino acids on 2,3‐
di‐O‐pentyl‐6‐O‐acyl
2005;1071(1‐2):59‐66.
cyclodextrins.
J
Chromatogr
A.
6. Blum W, Aichholz R. Gas chromatographic enantiomer
separation on tert‐butyldimethylsilylated β‐cyclodextrin
diluted in PS‐086. A simple method to prepare enantioselective
glass capillary columns. J High Resolut Chromatogr. 1990;13(7):
515‐518.
4 | CONCLUSION
7. Shitangkoon A, Vigh G. Systematic modification of the separation
selectivity of cyclodextrin‐based gas chromatographic stationary
phases by varying the size of the 6‐O‐substituents. J Chromatogr
A. 1996;738(1):31‐42.
It can be seen that chiral recognition of 1‐
phenylalkylamine derivatives by the MTBCD stationary
phase is governed by several factors simultaneously. The
size, polar property, and substitution position of a group
on the analyte structure as well as the separation temper-
ature can influence the resolution of the enantiomers for
each analyte differently. All enantiomers of analytes with
fluoro substitution on the aromatic ring showed good
enantioseparation by the MTBCD stationary phase, and
they could be completely resolved in a reasonable analysis
time. Meta‐substitution on the aromatic ring seemed to
provide adequate enantioseparation regardless of the type
of substituent. Small functional groups (such as fluoro,
chloro, and bromo) substituted at ortho‐position of the
aromatic ring tend to improve enantioseparation, while
a larger ethyl group substituted at the stereogenic center
tends to hinder enantioseparation.
8. Takahisa E, Engel KH. 2,3‐Di‐O‐methoxymethyl‐6‐O‐tert‐
butyldimethylsilyl‐β‐cyclodextrin, a useful stationary phase for
gas chromatographic separation of enantiomers. J Chromatogr
A. 2005;1076(1‐2):148‐154.
9. Bicchi C, Cagliero C, Liberto E, et al. New asymmetrical per‐
substituted cyclodextrins (2‐O‐methyl‐3‐O‐ethyl‐ and 2‐O‐ethyl‐
3‐O‐methyl‐6‐O‐t‐butyldimethylsilyl‐β‐derivatives) as chiral
selectors for enantioselective gas chromatography in the flavour
and fragrance field. J Chromatogr A. 2010;1217(7):1106‐1113.
10. Berthod A, Li W, Armstrong DW. Multiple enantioselective
retention mechanisms on derivatized cyclodextrin gas chromato-
graphic chiral stationary phases. Anal Chem. 1992;64(8):873‐879.
11. Beck T, Nandzik J, Mosandl A. Diluted modified cyclodextrins as
chiral stationary phases in capillary gas chromatography‐
Octakis(2,3‐di‐O‐propionyl‐6‐O‐tert‐butyldimethylsilyl)‐γ‐cyclo-
dextrin. J Microcol Sep. 2000;12(9):482‐492.
12. Nie MY, Zhou LM, Wang QH, Zhu DQ. Enantiomer separation
of mandelates and their analogs on cyclodextrin derivative chiral
stationary phases by capillary GC. Anal Sci. 2001;17(10):
1183‐1187.
ACKNOWLEDGMENTS
Financial support from the 90th Anniversary of
Chulalongkorn University Fund (Ratchadaphiseksomphot
Endowment Fund) is gratefully acknowledged. Professor
Gyula Vigh is greatly appreciated for providing the CD
derivative used in this study.
13. Špánik I, Oswald P, Krupčík J, Benicka E, Sandra P, Armstrong
DW. Evaluation of non‐polar interactions in chiral recognition
by alkylated β‐ and γ‐cyclodextrin chiral stationary phases.
J Sep Sci. 2002;25(1‐2):45‐52.
14. Bicchi C, Brunelli C, Cravotto G, Rubiolo P, Galli M, Mendicuti
F. Cyclodextrin derivatives in GC separation of racemates with
different volatilities. Part XIX: thermodynamic aspects of
enantioselective GC separation of some volatiles with γ‐cyclo-
dextrins 2,3‐substituted with methyl and acetyl groups. J Sep
Sci. 2003;26(9‐10):761‐770.
ORCID
Aroonsiri Shitangkoon
15. Špánik I, Kačeriaková D, Krupčík J, Armstrong DW. GC Separa-
tion of enantiomers of alkyl esters of 2‐bromo substituted
carboxylic acids enantiomers on 6‐TBDMS‐2,3‐di‐alkyl‐β‐ and
γ‐cyclodextrin stationary phases. Chirality. 2014;26(6):279‐285.
REFERENCES
1. Scriba GKE. Chiral recognition in separation science—an
update. J Chromatogr A. 2016;1467:56‐78.