What is the definition of ‘enantiomeric excess’? How may the enantiomeric excess of a compound be determined using a chiral chromatographic approach?

Enantiomeric excess (ee) is a measurement of the extent to which one enantiomer (mirror-image isomer) of a chiral compound is present in greater quantity than its counterpart in a mixture. It quantifies the degree of chirality or asymmetry in a sample.

Chiral chromatographic approaches are commonly used to determine the enantiomeric excess of a compound. Here's a general outline of how it's done:

Chiral stationary phase: In chiral chromatography, the stationary phase is made chiral. This means that the stationary phase itself possesses chirality, allowing it to selectively interact with one enantiomer over the other based on their stereochemistry.

Sample injection: The sample containing the mixture of enantiomers is injected into the chromatographic system.

Separation: As the sample passes through the chiral stationary phase, the enantiomers interact differently with the stationary phase due to their stereochemical differences. One enantiomer will have a stronger interaction with the stationary phase, causing it to elute (come out) from the chromatographic column later than the other enantiomer.

Detection: Enantiomers are detected as they elute from the chromatographic column. Various detection methods can be used, such as UV detection or mass spectrometry.

Quantification: The areas or heights of the peaks corresponding to each enantiomer in the chromatogram are measured. The enantiomeric excess can be calculated using the formula: