Optical purity :

The compound's optical purity is measure of its enantiomeric purity and is given in terms of the enantiomeric excess (ee) of it. A pure enantiomer would comprise an optical purity and enantiomeric excess of 100%. A fully racemized compound would comprise an optical purity of 0%. If the enantiomeric excess is 90%, it shows that 90% of the sample is pure enantiomer and the remaining 10% is a racemate consisting of equal amounts of each enantiomer (i.e. 5% + 5%). Hence the ratio of enantiomers in a sample comprising 90% optical purity is 95:5.