Lecture 7

Lecture 7

Chromatography Intro!

Compounds of interest stick

to sorbent

Solid Phase ExtractionLoad

(sample)

Compounds of interest

released from sorbent

Waste

Eluent(solvent)

Extract

Compounds of interest in a

plug

Chromatography

LoadSample

(injection)

Differential interaction with

stationary phase separates compounds in

time and space.

Detector

Mobile phase

Detector

Mobile phase

ChromatographyDefinition

Separation of components in a mixture based on the differential movement through a porous media under the influence of a mobile phase

First Chromatography Column

toluene

sample

What happens in a chromatographic column?

Gas Chromatography(GC)

Liquid Chromatography(LC)

Distillation Liquid-liquidextraction

Theoretical Plate

Silica support

Stationary phase

GC - gas chromatographyopen tubular columns

Gas (mobile phase)

Theoretical PlateLC - liquid chromatography

packed columns

Silica beads

Stationary phase

liquid (mobile phase)

Number of Theoretical Plates

N = L H

Length of the column

Height equivalent of a theoretical plate

Retention Factor

k’ = tR-tM

tM

= VR-VM

VM

1 < k’ < 10

Describes the strength of the interaction of a compound with the stationary phase

Compounds of interest stick

to sorbent

Solid Phase ExtractionLoad

(sample)

Compounds of interest

released from sorbent

Waste

Eluent(solvent)

Extract

k’ > 1000 k’ < 0.001

Compounds of interest in a

plug

Chromatography

LoadSample

(injection)

Differential interaction with

stationary phase separates compounds in

time and space.

Detector

Mobile phase

Detector

Mobile phase

1 < k’ < 10

Retention Factor (k’)Describes the strength of the interaction of a

compound with the stationary phase

k’ = tR-tM

tM=

VR-VM

VM

1 < k’ < 10

k’ = tR-tM

tM=

VR-VM

VM

1 < k’ < 10

Retention Factor (k’)

Effect of k’ on Selectivity and Resolution in LC

Dong, M. Today’s Chemist at Work. 2000, 9(2), 46-48.

SelectivityDescribes differential mobility of 2 compounds

= k’2

k’1

= K2

K1

ResolutionDescribes how well 2 compounds are separated

Rs = 2(tR2-tR1)

tw1+tw2

ResolutionDescribes how well 2 compounds are separated

Rs = 14

N1/2 (-1)k’

1+k’( )efficiency selectivity

retention