Can I calculate ee from chiral HPLC peak areas?

Yes. If peak areas are proportional to amounts (same response factor), ee = |AreaR − AreaS|/(AreaR + AreaS) × 100%.

How do I use optical rotation to estimate ee?

If measurements are made under the same conditions, ee(%) ≈ (αobs/αpure) × 100%. The sign indicates which enantiomer is major.

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Enantiomeric Excess (ee) Calculator

Q: What does ee = 0% mean?

ee = 0% means the mixture is racemic: equal amounts of both enantiomers.

Q: What does ee = 100% mean?

ee = 100% means the sample is a single enantiomer (no detectable amount of the other, in the idealized calculation).

Calculate enantiomeric excess (ee) from R/S percentages, chiral HPLC/GC peak areas, or optical rotation. Includes steps, quick picks, and a mini R vs S visual.

Background

Enantiomeric excess tells you how much one enantiomer dominates the other. A racemic mixture has ee = 0%, while a pure enantiomer has ee = 100%.

Enter inputs

Input mode

R% and S% (composition)

Peak areas (Area_R, Area_S)

Optical rotation (α_obs, α_pure)

Pick the data you actually have — we’ll compute ee and the major enantiomer.

Composition

If R% + S% ≠ 100, we’ll normalize automatically (common when values are unscaled).

Peak areas

We treat areas as proportional to amount (same response factor assumption).

Optical rotation

The sign (+/−) matters. Use the rotation of a pure enantiomer under the same conditions.

Options

Round results

Show step-by-step

Show mini visualization

Quick picks

Chips fill values and solve immediately.

Result:

No results yet — enter inputs and click Calculate.

How to use this calculator

Choose an input mode: Composition (R%/S%), Peak areas, or Optical rotation.
Enter your two values (R and S, or AreaR and AreaS, or αobs and αpure).
Click Calculate to get ee (%), major enantiomer, and enantiomeric ratio (ER).
Use Quick picks to sanity-check: racemic (50/50) should give ee = 0%.

How this calculator works

For composition or peak areas, we treat the two numbers as proportional amounts and compute: ee(%) = |R − S|/(R + S) × 100.
The major enantiomer is simply the larger of the two values (R or S).
The enantiomeric ratio is reported as major : minor (approx).
For optical rotation, we estimate: ee(%) ≈ (αobs/αpure) × 100 (same conditions).

Note: For optical rotation, “which enantiomer is major” depends on your reference convention (what αpure corresponds to). This calculator reports whether αobs matches αpure in sign.

Formula & Equation Used

Enantiomeric excess:

$e e (%) = \frac{| R - S |}{R + S} \times 100$

From optical rotation:

$e e (%) \approx \frac{α_{obs}}{α_{pure}} \times 100$

Enantiomeric ratio: ER = major : minor

Example Problems & Step-by-Step Solutions

Example 1 — Composition (R% / S%)

Suppose a mixture is 60% R and 40% S.
ee = |60 − 40|/(60 + 40) × 100 = 20%. The major enantiomer is R, and the ratio is 60:40 = 1.5:1.

Example 2 — Peak areas (chiral HPLC/GC)

AreaR = 845, AreaS = 155.
ee = |845 − 155|/(845 + 155) × 100 = 69%. Major = R. ER ≈ 845:155 ≈ 5.45:1.

Example 3 — Optical rotation

Observed rotation αobs = +8.4, pure enantiomer rotation αpure = +12.0.
ee ≈ (8.4/12.0)×100 = 70%. Because the signs match (+/+), the major is “same as αpure” under this convention.