Introduction

The separation of enantiomers (optical isomers) by capillary gas chromatography on a chiral stationary phase (CSP) was discovered by Gil-Av and coworkers at the Weizmann Institute of Science, Israel, in 1966. At the outset of this work, according to Gil-Av, this topic was in a 'state of frustration'. Nobody believed it could be done. In fact, people were convinced that there could not possibly be a large enough difference in the interaction between the d-and l-solute with an asymmetric solvent. This was the feeling people had, even those known as unorthodox thinkers. This view had also some experimental basis, because a number of communications had been published, in which it was claimed that such resolutions could be effected, but nobody was able to reproduce these results, and some of them were shown to be definitely wrong.

Today, almost a reversal of this situation exists. According to the GC Chirbase data bank, for most volatile racemic compounds of a variety of different chemical classes, ranging from apolar to polar, an appropriate CSP is available and 22 200 chiral separations by gas chromatography (GC) of 7637 analytes on 684 CSPs (120 are commercialized) have been reported up to the end of 1997.

Three principal CSPs are currently employed; these undergo hydrogen bonding, coordination and inclusion. Modified a-, ft- and y-cylodextrins have proved to be the most versatile and universal CSPs in GC. Anchoring the CSPs to a polysiloxane backbone leads to Chirasil-type stationary phases with improved temperature stability, efficiency and robustness. Immobilization of Chirasil-type stationary phases on the inner column wall furnishes chemically bonded CSPs. Because of the high efficiency, sensitivity and speed, chiral separation by high resolution capillary GC represents a versatile and attractive method for enan-tiomer analysis. However the prerequisites of the method, i.e. volatility, thermal stability and resolv-ability of the chiral analytes, restrict its universal use.

The main application of chiral separations by GC is concerned with the precise determination of enan-tiomeric compositions of chiral research chemicals, intermediates, auxiliaries, metabolites, precursors, drugs, pesticides, fungicides, herbicides, pheromones, flavours and fragrances. As the insight into chiral-ity-activity relationships steadily improves and, as a consequence, legislation on chiral compounds becomes more stringent, the development of reliable methods for the determination of the enantiomeric excess up to 99.9% is of great importance (% enantiomeric excess = 100(R — S)/(R + S), where R is the major enantiomer and S the minor enantiomer). This goal is readily met by enantioselective GC.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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