For a mixture of (+)- and (-)-enantiomers, with composition given as the mole or weight fractions F(+) and F(-) (where F(+) + F(-) = 1) the enantiomer excess is defined as |F(+)- F(-)| (and the percent enantiomer excess by 100.|F(+)- F(-)|). Frequently this term is abbreviated as e.e.
See: optical purity
Source:
PAC, 1996, 68, 2193. 'Basic terminology of stereochemistry (IUPAC Recommendations 1996)' on page 2207 (https://doi.org/10.1351/pac199668122193)