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Chiral Separations in GC Outline • Introduction • Theory • Advantages and Disadvantages • Applications • Conclusions • References 2 Chiral Separations in GC Introduction: • One of the limitations of conventional GC –Cannot be used to separate enantiomers. –Enantiomers are nonsuperimposable mirror-image molecules. –Since they have identical properties, they elute at the same time in non-chiral GC. • However diastereomers can be separated using chromatography: –Different chromatographic properties –Different retention times 3 Chiral Separations in GC Introduction: • Chiral separations in GC can be achieved via: –Using a derivatization procedure with a chiral auxiliary –Using mobile phase additive to form diastereomer complexes which then separated on an achiral stationary phase. –Using a non-racemic chiral stationary phase (CSP) 4 Chiral Separations in GC Introduction: • In the late 1960s, chiral separation in GC was a challenging problem among scientists. • In 1967, Prof. E. Gil-Av was successfully demonstrated chiral separation for L- and D-amino acid esters with lauryl ester of N-trifluoroacetyl-L-isoleucine as CSP. • In 1977, the first polysiloxane bonded CSP, Chirasil-VAL (thermal stability > 200⁰C) was developed by H. Frank, G. Nicholson and E. Bayer. • In 1987, the first capillary column coated with cyclodextrins was invented by Prof. W. A. Konig in cooperation with Macherey-Nagel. • In the early of 1980s, the successful separations of o-, m-, p-xylenes and ethylbenzene on a cyclodextrins CSP were published. 5 Chiral Separations in GC Theory: The main purpose of chiral separations is to determine the precise enantiomeric compositions or enantiomeric excess: % ee = 100(R-S)/(R+S) with R= major enantiomer S= minor enantiomer of chiral analytes 6
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