Introduction to Chromatography

Separate a complex mixture into individualComponents based on interactions between a Mobile phase and a stationary phase

Amp = Asp

K = [A]sp / [A]mp

Chromatographic system: column plus detector

Chromatogram: Plot of Detector Response as a function of elution time

GCLCHPLCTLCSFCICSize ExclusionCZEAffinity

Chromatography: Different Types

http://www.youtube.com/watch?v=08YWhLTjlfo

http://www.youtube.com/watch?v=kz_egMtdnL4

Sp: solidMp: liq or gasEquil btwn ads. state and liq-gas

Adsorption

Partition

Sp: liq on solidMp: liq or gasEquil btwn liq. state and liq-gas

Ion ExchangeSp: ion exch. resinMp: liqElectrostatic attractions

Sp: porous gelMp: liq

Permeation into the gel

Molecular Exclusion

Affinity

Sp: solid with immobilized molecMp: liqSpecific interactions

SFCSp: solidMp: SC fluid

Partition btwn fluid and adsorbent

Describe the separation

tR = retention time

tm = dead time

tR’ = adjusted retention time

k’ = capacity factor

Describes migration rate of a solute

Larger k’, longer the solute is retained

Good values: 1-5

k’ = (tR - tm) / tmk’ = K (Vs/Vm)

Describe the separation

= selectivity factor

How well the column separates 2 species

Larger the number, the greater the sepn btwn the two

Always greater than 1

= KB / KA

= k’B / k’

A

= (tR,B – tm) / (tR,A – tm)

Describe the separation

Efficiency of a Separation

Two Factors1- elution times btwn peaks2- how broad the peaks are

Qualitative

Eddy DiffusionLongitudinal DiffusionRate of Mass Transfer

Eddy Diffusion

Multiple pathsIndependent of flow rateDepends on particle diameter…

Longitudinal DiffusionConcentration gradientsGreater flow less spreadingDepends on Diffusion Coeff….

EquilibrationGreater flow rate more spreadingDepends on Diff. Coeff, stationary phase…

Rate of Mass Transfer

Quantitative Description: N,H,R

Examine Peaks

R = tR / Wavg

R = (tR,2 – tR,1) / Wavg

R > 1.5 is good

Quantitative Description: N,H,R

Number of Theoretical Plates (N)

N = L/H N = 16tR2 / Wb

2

Plate Height (H)

Height equivalent to a theoretical plateSmall value is good

Resolution

RN k

ks

avg

4

1

1

2

'

'

Large - good

Van Deemter Equation

H ~ A + B/ + C

H