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Chapter 26

Chapter 26. Intro to Chromatography CHM 411 Spring 2013 Suroviec. I. Classification of Chromatographic Methods. Method for separating components of a mixtures based on their relative affinities for 2 different phases.

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Chapter 26

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  1. Chapter 26 Intro to Chromatography CHM 411 Spring 2013 Suroviec

  2. I. Classification of Chromatographic Methods • Method for separating components of a mixtures based on their relative affinities for 2 different phases

  3. Resolution of Gaussian peaks of equal area and amplitude. Dashed lines show individual peaks, and solid lines are the sum of two peaks. Overlapping area is shaded.

  4. II Migration Rates of Solutes A. Distribution constants

  5. B. Retention Time

  6. II. Migration Rates of Solutes

  7. A. Relating retention time

  8. B. Retention factor

  9. C. Relative migration rates • We want the peaks to be base-line resolved.

  10. III. Zone broadening • Ideal peak shape is gaussian • Variables: number of phase transfers, residence time in phases

  11. A. Plate theory

  12. B. Rate Theory • Explains why peaks broaden consider solute band moving though the column

  13. C. Van deemter Equation A = multiple flow paths

  14. B/u = longitudinal diffusion Solute continuously diffuses away from the concentrated center of its zone

  15. Csu + Cmu = mass transfer coefficient The slower the linear flow the more complete the equilibration and the less the zone broadening

  16. Application of the van Deemter eqn. to gas chromatography

  17. IV. Optimizing Performance • Reduce zone broadening • Alter relative migration rates

  18. A. Resolution • Calculate efficiency needed for required resolution

  19. B. Ways to increase performance 1. Increase N 2. Change k’ 3. Change selectivity factor

  20. C. General elution problem

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