1. A guide for A level students KNOCKHARDY PUBLISHING
CHROMATOGRAPHY
A guide for A level students
2008 SPECIFICATIONS
KNOCKHARDY PUBLISHING

2. CHROMATOGRAPHY www.knockhardy.org.uk/sci.htm INTRODUCTION
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3. CHROMATOGRAPHY
Chromatography is used to separate and analyse small amounts of mixtures
Methods involve a stationary phase and a mobile phase.
There are several forms of chromatography

4. CHROMATOGRAPHY
Chromatography is used to separate and analyse small amounts of mixtures
Methods involve a stationary phase and a mobile phase.
There are several forms of chromatography
TYPE STATIONARY PHASE MOBILE PHASE
paper solid (filter paper) liquid
thin layer (tlc) solid (silica) liquid
column solid (silica) liquid
high pressure liquid (hplc) solid (silica) liquid
gas liquid (glc) solid or liquid gas

5. PAPER CHROMATOGRAPHY Stationary phase chromatography paper
Mobile phase suitable solvent (water, ethanol, organic solvent)
Separation As the solvent moves up the paper it dissolves the
components and moves them up the paper. The
more soluble a component is, the further it moves.
Place small a spot of the mixture to be analysed (and any possible component for comparison purposes) on the paper. Dip the paper in the solvent.

6. PAPER CHROMATOGRAPHY Stationary phase chromatography paper
Mobile phase suitable solvent (water, ethanol, organic solvent)
Separation As the solvent moves up the paper it dissolves the
components and moves them up the paper. The
more soluble a component is, the further it moves.
Place small a spot of the mixture to be analysed (and any possible component for comparison purposes) on the paper. Dip the paper in the solvent.
Allow the solvent to rise up the paper. Each component dissolves in the solvent. Those which are more soluble travel further up the paper.

7. Finished chromatogram
PAPER CHROMATOGRAPHY
Stationary phase chromatography paper
Mobile phase suitable solvent (water, ethanol, organic solvent)
Separation As the solvent moves up the paper it dissolves the
components and moves them up the paper. The
more soluble a component is, the further it moves.
Place small a spot of the mixture to be analysed (and any possible component for comparison purposes) on the paper. Dip the paper in the solvent.
Allow the solvent to rise up the paper. Each component dissolves in the solvent. Those which are more soluble travel further up the paper.
Finished chromatogram

8. PAPER CHROMATOGRAPHY Rf value Under similar conditions, a component
should always travel at the same speed.
Its identity can be found by comparing
the distance it moves relative to the solvent.
Rf = distance travelled by the component = Y
distance travelled by the solvent X X Y

9. PAPER CHROMATOGRAPHY Rf value Under similar conditions, a component
should always travel at the same speed.
Its identity can be found by comparing
the distance it moves relative to the solvent.
Rf = distance travelled by the component = Y
distance travelled by the solvent X
Comparison can be a problem if…
a) components have similar Rf values
b) the unknown substance is new and there is
no previous chemical to compare it with X Y

10. THIN LAYER CHROMATOGRAPHY
Stationary phase silica mounted on a glass plate
Mobile phase suitable organic solvent
Separation similar technique to paper chromatography
Limitations similar to paper chromatography
Advantages faster than paper chromatography
works with very small samples
will separate a wide range of mixtures

11. COLUMN CHROMATOGRAPHY
Stationary phase silica
Mobile phase suitable organic solvent
Separation components interact with the stationary
phase to different extents A B B C

12. COLUMN CHROMATOGRAPHY
Stationary phase silica
Mobile phase suitable organic solvent
Separation components interact with the stationary
phase to different extents
Method
• a chromatography column is filled with solvent and silica
• drops of the mixture are placed on top of the silica - A
• the tap is opened to allow the solvent to flow out
• additional solvent is added on top to replace that leaving
• components travel through at different rates and separate - B
• batches of solvent are collected at intervals - C
• the solvent in each batch is evaporated to obtain components A B B C

13. HIGH PRESSURE LIQUID CHROMATOGRAPHY (HPLC)
A better form of column chromatography. Instead of draining down through the stationary phase, the solvent is forced through under high pressure.
Stationary phase silica
Mobile phase suitable solvent
Separation similar to column chromatography

14. HIGH PRESSURE LIQUID CHROMATOGRAPHY (HPLC)
A better form of column chromatography. Instead of draining down through the stationary phase, the solvent is forced through under high pressure.
Stationary phase silica
Mobile phase suitable solvent
Separation similar to column chromatography
Method • a sample is injected
• solvent and sample are pushed through under pressure
• different compounds have different retention times
• output can be detected by compounds absorbing UV
• can be connected to a mass spectrometer

15. HIGH PRESSURE LIQUID CHROMATOGRAPHY (HPLC)
A better form of column chromatography. Instead of draining down through the stationary phase, the solvent is forced through under high pressure.
Stationary phase silica
Mobile phase suitable solvent
Separation similar to column chromatography
Method • a sample is injected
• solvent and sample are pushed through under pressure
• different compounds have different retention times
• output can be detected by compounds absorbing UV
• can be connected to a mass spectrometer
Advantages • it is fast
• the path is short - usually under 30cm
• it gives better separation

16. GAS LIQUID CHROMATOGRAPHY (GLC)
Stationary phase liquid adsorbed on an inert solid support
Mobile phase gas
Method
• a very small amount of a sample
is injected into the machine
• the injector is contained in an oven
• the sample boils and is carried along
a thin column by an inert carrier gas
• column contains a liquid stationary phase, adsorbed onto an inert solid
• the time taken to travel through the tube will depend on how much time is
spent moving with the gas rather than being attached to the liquid.

17. GAS LIQUID CHROMATOGRAPHY (GLC)
Retention time The time taken for a compound to travel through the
column to the detector.
It is measured from the time the sample is injected to
the time its peak shows maximum height.

18. GAS LIQUID CHROMATOGRAPHY (GLC)
Retention time The time taken for a compound to travel through the
column to the detector.
It is measured from the time the sample is injected to
the time its peak shows maximum height.
For a particular compound, the retention time depends on...
boiling point high boiling point = long retention time

19. GAS LIQUID CHROMATOGRAPHY (GLC)
Retention time The time taken for a compound to travel through the
column to the detector.
It is measured from the time the sample is injected to
the time its peak shows maximum height.
For a particular compound, the retention time depends on...
boiling point high boiling point = long retention time
solubility in the liquid phase greater solubility = long retention time

20. GAS LIQUID CHROMATOGRAPHY (GLC)
Retention time The time taken for a compound to travel through the
column to the detector.
It is measured from the time the sample is injected to
the time its peak shows maximum height.
For a particular compound, the retention time depends on...
boiling point high boiling point = long retention time
solubility in the liquid phase greater solubility = long retention time
ANIMATION

21. GAS LIQUID CHROMATOGRAPHY (GLC)
Detection • there are several ways to detect components
• most involve destruction of the sample
• one method is an FID - flame ionisation detector
The FID • as a component exits, it is burned in a hydrogen flame
• ions are produced in the flame
• a detector produces an electric current
• greater the amount of a component = larger current
• the current can be represented by a chromatogram
• as the component is destroyed, GCMS doesn’t use FID

22. GAS LIQUID CHROMATOGRAPHY (GLC)
Interpretation
• each compound in the mixture will produce a peak
• the areas under the peaks are proportional to the amount of a compound
• retention times are used to identify compounds – they are found out by
putting known compounds through the system under similar conditions
The area under a peak is proportional to the amount present.
Because each compound responds differently, the machine is calibrated beforehand to show the actual mount.
Each component has a different retention time.

23. GAS CHROMATOGRAPHY – MASS SPECTROMETRY (GCMS)
Process When a peak is detected in gas chromatography, some of
the component is sent to a mass spectrometer
A mass spectrometer has three main parts...

24. GAS CHROMATOGRAPHY – MASS SPECTROMETRY (GCMS)
Process When a peak is detected in gas chromatography, some of
the component is sent to a mass spectrometer
A mass spectrometer has three main parts...
Ioniser - the sample is bombarded with electrons and ionised
- a positive molecular ion is formed
- the molecular ion can break up into smaller ions
- positive ions are accelerated towards the analyser

25. GAS CHROMATOGRAPHY – MASS SPECTROMETRY (GCMS)
Process When a peak is detected in gas chromatography, some of
the component is sent to a mass spectrometer
A mass spectrometer has three main parts...
Ioniser - the sample is bombarded with electrons and ionised
- a positive molecular ion is formed
- the molecular ion can break up into smaller ions
- positive ions are accelerated towards the analyser
Analyser - positive ions separate according to mass/charge ratio
- higher mass/charge ratio = smaller deflection

26. GAS CHROMATOGRAPHY – MASS SPECTROMETRY (GCMS)
Process When a peak is detected in gas chromatography, some of
the component is sent to a mass spectrometer
A mass spectrometer has three main parts...
Ioniser - the sample is bombarded with electrons and ionised
- a positive molecular ion is formed
- the molecular ion can break up into smaller ions
- positive ions are accelerated towards the analyser
Analyser - positive ions separate according to mass/charge ratio
- higher mass/charge ratio = smaller deflection
Detector - records the identity and abundance of each ion
- compounds have a unique mass spectrum
- the final peak (molecular ion) gives the molecular mass

27. GAS CHROMATOGRAPHY – MASS SPECTROMETRY (GCMS)
Process When a peak is detected in gas chromatography, some of
the component is sent to a mass spectrometer
A mass spectrometer has three main parts...
Ioniser - the sample is bombarded with electrons and ionised
- a positive molecular ion is formed
- the molecular ion can break up into smaller ions
- positive ions are accelerated towards the analyser
Analyser - positive ions separate according to mass/charge ratio
- higher mass/charge ratio = smaller deflection
Detector - records the identity and abundance of each ion
- compounds have a unique mass spectrum
- the final peak (molecular ion) gives the molecular mass

28. For more information, consult the notes on ‘Mass Spectrometry’
A MASS SPECTROMETER
ANALYSER
DETECTOR
ION SOURCE
IONISATION
gaseous atoms are bombarded by electrons from an electron gun and are IONISED
sufficient energy is given to form ions of 1+ charge
ACCELERATION
ions are charged so can be ACCELERATED by an electric field
DEFLECTION
charged particles will be DEFLECTED by a magnetic or electric field
DETECTION
by electric or photographic methods
For more information, consult the notes on ‘Mass Spectrometry’

29. CHROMATOGRAPHY A guide for A level students
© 2009 JONATHAN HOPTON & KNOCKHARDY PUBLISHING