Specific Rotation Calculation

 

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Calculating a Compound's Specific Rotation

PDR-Chiral has created a Specific Rotation Calculation Worksheet for conveniently calculating a compound's specific rotation. This worksheet can be downloaded by clicking on the Hyperlink above. To perform the calculation, the operator simply measures the optical rotation of a known amount of a pure enantiomer using a separation technique such as HPLC, SFC, FIA or CE. Themost convenient method uses the separation system in combination with a laser polarimeter, such as the one offered by PDR-Chiral Inc. If we know the amount of the chiral compound injected, the chromatographic peak profile and the internal dimensions of the polarimeter's flow cell, we can easily calculate the compound's specific rotation.

The following instructions explain how to use the Specific Rotation Calculation Worksheetorksheetorksheet. The downloadable worksheet includes an example using L L -(-)-phenylalanine but can be applied to virtually any optically active enantiomer. A downloadable copy of the instructions is also available by clicking on the Hyperlink above. We hope that this tool will be of assistance in your work with chiral compounds. Please send us any comments that you may have in order that we may continually improve our "Chiral Resource Center's Tools for Chiral Chemists".

 Instructions for Calculating Specific Rotation

  1. Perform three injections of the designated test mixture. We typically use 0.1 mg/ml L-(-)-phenylalanine with water as the eluent and a 15 cm CN column.

  2. Insert the appropriate values for Date, detector Serial Number and Test Compound into the Specific Rotation Calculation Worksheet. Also enter the Injection Volume and Injection Concentration.

  3. From the first chromatogram, determine the Peak Start, Peak Apex and Peak End and enter them into the appropriate spreadsheet cells.

  4. The spreadsheet will then calculate the Signal at Half Height and automatically compensate for any drift of the detector baseline.

  5. Using the Signal at Half-Height, determine the retention times for the peak Front at Half Height and Tail at Half-Height. Insert these values into the spreadsheet.

  6. Repeat steps 3 through 5 for the second and third injections.

  7. The spreadsheet will calculate the average Peak Width at Half Height for the three injections.

  8. Insert the Flow Rate, Flow Cell Volume and Flow Cell Length into the spreadsheet.

  9. The Gaussian Probability Variable is automatically calculated.

  10. .  Use the Gaussian Probability Variable and the Probability Factor Lookup Table to determine the Probability Factor. Move vertically down column A to locate the first decimal place and then move horizontally across the table to locate the second decimal place. Extrapolate between points to accurately determine the correct value. Enter the value as the Probability Factor.

  11. .  The Specific Rotation is automatically calculated using the Gaussian Fraction, Injected Mass, Flow Cell Volume, Flow Cell Length and the Peak Height average for the three injections.

  12. .  Save, print, sign and date the completed Specific Rotation Calculation Worksheet as appropriate.

 

Send questions or comments about this web site to  [email protected].
Last modified: November 08, 1999

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