ABSTRACT
In an effort to simultaneously enantioseparate racemic unfunctionalized alkanes and racemic alpha-amino acid derivatives by gas chromatography (GC) in forthcoming experiments related to the search for extraterrestrial homochirality, the two versatile modified cyclodextrin (CD) selectors octakis(6-O-methyl-2,3-di-O-pentyl)-gamma-cyclodextrin (Lipodex G) and heptakis(2,3-di-O-methyl-6-O-tert-butyldimethylsilyl)-beta-cyclodextrin were dissolved in a polysiloxane and the mixed binary chiral selector system was coated onto a 50m x 0.25 mm i.d. fused silica capillary column. Whereas the former CD selector enantioseparates racemic unfunctionalized alkanes the latter CD selector preferentially resolves N-(O,S)-trifluoroacetyl-alpha-amino acid alkyl esters. With both CD selectors employed as mixed binary chiral selector system present in one chiral stationary phase (CSP), the simultaneous gas chromatographic enantioseparation of racemic alkanes and of racemic derivatized alpha-amino acids is achieved in a single temperature-programmed run. Also for other classes of racemic compounds, the scope of enantioseparation could be extended as compared to the conventional use of the single CD selectors in GC.
Subject(s)
Alkanes/isolation & purification , Amino Acids/isolation & purification , Chromatography, Gas/methods , Cyclodextrins/chemistry , Chromatography, Gas/instrumentation , StereoisomerismABSTRACT
In the context of the Titan Chiral Organics Explorer (TCOE) mission, the theoretical and practical aspects of the miniaturization of enantioselective gas chromatography are discussed. The use of short columns (0.5-10 m) with a conventional inside diameter of 250 microm is proposed. The inside diameter should be increased for vacuum-assisted GC-MS using a restrictor at the inlet of the capillary. The feasibility of cryogenic enantioselective gas chromatography is demonstrated. The hitherto elusive use of chiral mobile phase additives in enantioselective gas chromatography is proposed.
ABSTRACT
Efficient enantiomer separation by pressure-assisted, micro-packed capillary electrochromatography (CEC) has been carried out using a permethyl-beta-cyclodextrin-modified silica support (PM-beta-CD-silica). When comparing this method with micro-packed-high-performance liquid chromatography in the single-column-mode, CEC displays higher column efficiencies (about three times higher theoretical plate numbers at comparable elution times). The pressure support (about 10 bar), applied to avoid bubble formation, has a negligible influence on elution times in CEC. The influence of the type and composition of organic modifiers is described.
