Chiral Purity (enantiomer excess) for HPLC

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Discussion Overview

The discussion revolves around calculating chiral purity, specifically enantiomer excess (ee), using High-Performance Liquid Chromatography (HPLC) data, including chromatograms and peak areas. The conversation includes both practical calculations and historical methods.

Discussion Character

  • Technical explanation
  • Exploratory
  • Homework-related

Main Points Raised

  • One participant asks how to calculate chiral purity using peak area from HPLC results.
  • Another participant humorously suggests a historical method involving weighing paper to determine purity based on mass differences.
  • A third participant explains the calculation of enantiomer excess (ee) using the areas of both enantiomers, providing a formula and examples of how to compute ee based on peak area ratios.
  • There is a note that if the desired enantiomer is different, the calculation needs to be adjusted accordingly, and a negative ee indicates the production of the undesired product.

Areas of Agreement / Disagreement

Participants present various methods and calculations without reaching a consensus. The humorous historical method contrasts with the technical explanation of calculating ee, indicating differing approaches to the problem.

Contextual Notes

The discussion does not clarify assumptions regarding the accuracy of the HPLC measurements or the definitions of enantiomers used in the calculations.

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[SOLVED] Chiral Purity (enantiomer excess) for HPLC

Hello!

When I use HPLC to test Chiral Purity, obtain chromatogra and peak area. How do I calculate with Peak area?

thanks!
 
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cwj7316 said:
Hello!

When I use HPLC to test Chiral Purity, obtain chromatogra and peak area. How do I calculate with Peak area?

thanks!

LOL you want to know how they used to do it back in the day? Weigh the piece of paper your spectrum is on. Cut out the peaks and weigh the paper. You should be able to tell by the difference in mass how pure your compound is.
 
If you are given the areas of both enantiomers (or even epimers), the ee is calculated by first summing the areas of both peaks and determining their relative ratios. R and S, for example where R+S=1 and ratio of R=R/(R+S). ee is defined as {(R-S)/(R+S)}*100. If the areas are 0.6:0.4, the ee is 20%. If the areas are 0.98:0.02, the ee would be 0.96. In this example the desired enantiomer is R. If it is S in your case, just switch it around. If you get a negative number, the reaction produces an ee of the undesired product.
 
Thanks gravenewworld and chemisttree.
 

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