Intro to Chromatography CHM 480 Suroviec Chapter 26 Intro to Chromatography CHM 480 Suroviec

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

Resolution of Gaussian peaks of equal area and amplitude 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.

II Migration Rates of Solutes A. Distribution constants

B. Retention Time

II. Migration Rates of Solutes

A. Relating retention time

B. Retention factor

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

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

A. Plate theory

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

C. Van deemter Equation A = multiple flow paths

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

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

Application of the van Deemter eqn. to gas chromatography

IV. Optimizing Performance Reduce zone broadening Alter relative migration rates

A. Resolution Calculate efficiency needed for required resolution

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

C. General elution problem