1. 1.1 General description - Sample dissolved in and transported by a mobile phase - Some components in sample interact more strongly with stationary phase and are more strongly retained - Sample separated into zones or bands 1.2 Classification (based one the types of mobile and stationary) -Gas chromatography (GC) - Liquid chromatography (LC) - Supercritical fluid chromatography (SFC)

2. Classification  based on the types of mobile and stationary phases

3. 1.3 Elution chromatography: Flushing of sample through column by continual mobile phase addition - only eluent (portion of sample in mobile phase) moves down - migration rate  fraction of time spent in mobile phase Fig. 26-1 (p.764) (a) The separation of a mixture of components A and B by column elution chromatography, (b) the output of the signal detector

4. Fig. 26-2 (p.765) Concentration profiles of solute bands A and B at two different times in their migration down the column. - Chromatogram (concentration versus elution time) - More strongly retained species elutes last (elution order) - Analyte is diluted during elution (dispersion) - Zone broadening proportional to elution time

5. - Adjust migration rates for A and B (increase band separation) - Adjust zone broadening (decrease band spread) Fig. 26-3 (p.765) Two-component chromatogram illustrating two methods for improving overlapping peaks.

6. 2.1 Distribution constant Analyte A in equilibrium with two phases

7. t M time for unretained species (dead time), same rate as mobile phase molecules average migration rate t R retention time for retained species average migration rate Ideally: t R independent of volume injected, produces a Gaussian peak Fig. 26-4 (p.767) A typical chromatography for a two component mixture. 2.2 Retention time

8. 3.1 Rate theory of chromatography - Individual molecule undergoes “random walk”, and many thousands of adsorption/desorption processes. - Some travel rapidly while other lag  add up to give Gaussian peak (like random errors) - Breadth of band increases down column because of more time - Zone broadening is affecting separation efficiency – high efficiency requires less broadening

9. 3.2 Column efficiency N: number of plates L: length of column H: height of 1 theoretical plate Plates are only theoretical – column efficiency increase with N Fig. 26-6 (p.770) Definition of H. Efficient column has small plate height – less zone broadening

10. Experimentally, H and N can be approximated from the width of the base of chromatographic peak. Fig. 26-7 (p.770) Determination of N.

11. 3.3 Kinetic variables affecting column efficiency (H) 3.3.1 Mobile phase velocity -Higher mobile phase velocity, less time on column, less zone broadening -However, plate height H also changes with flow rate Fig. 26-7 (p.770) Effect of mobile-phase flow on plate height for GC.

12. 3.3.2 van Deemter Equation A: multipath term - Molecules move through different paths - Larger difference in pathlength for larger particles - At low flow rates, diffusion allows particles to switch between paths quickly and reduces variation in transit time Fig. 26-9 (p.773) Typical pathways of two molecules during elution.

13. B/  : Longitudinal diffusion term - Diffusion from central zone to front and tail - Proportional to analyte diffusion coefficient - Inversely proportional to flow rate - high flow, less time for diffusion C  :Mass transfer coefficients (C S and C M ) - C S is rate for adsorption onto stationary phase - C M is rate for analyte to desorb from stationary phase - Effect proportional to flow rate – at high flow rates less time to approach equilibrium Fig. 26-10 (p.774) van Deemter plot.

14. Column resolution Fig. 26-12 (p.776) Separation at three resolution values - u (linear flow rate): low flow rate favors increased resolution (van Deemter plot) -H (plate height) (or N number of plates): use smaller particles, lengthen column, reduce viscosity of mobile phase (diffusion) -  (selectivity factor): vary temperature, composition of column/mobile phase - k A (retention factor): vary temperature, composition of column/mobile phase

15. Fig. 26-15 (p.780) The general elution problem in chromatography General elution problem: for multiple components, conditions rarely optimum for all components. 1. Change liquid mobile phase composition – gradient elution or solvent programming 2. Change temperature for gas chromatography – temperature programming

16. Section 26E p781 (Reading assignment)