1. A guide for GCSE students KNOCKHARDY PUBLISHING
ANALYSING SUBSTANCES
A guide for GCSE students
2010 SPECIFICATIONS
KNOCKHARDY PUBLISHING

2. ANALYSING SUBSTANCES INTRODUCTION www.knockhardy.org.uk
This Powerpoint show is one of several produced to help students understand selected GCSE Chemistry topics. It is based on the requirements of the AQA specification but is suitable for other examination boards.
Individual students may use the material at home for revision purposes and it can also prove useful for classroom teaching with an interactive white board.
Accompanying notes on this, and the full range of AS and A2 Chemistry topics, are available from the KNOCKHARDY WEBSITE at...
All diagrams, photographs and any animations in this Powerpoint are original and created by Jonathan Hopton. Permission must be obtained for their use in any work that is distributed for financial gain.
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3. ANALYSING SUBSTANCES CONTENTS What is chromatography?
Paper chromatography
Gas liquid chromatography
Mass spectrometry
Questions
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4. CHROMATOGRAPHY
Chromatography is used to separate and analyse small amounts of mixtures
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5. CHROMATOGRAPHY
Chromatography is used to separate and analyse small amounts of mixtures
Methods involve a stationary phase (stays where it is)
and a mobile phase (moves)
There are several forms of chromatography
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6. However, they all work in the same way
CHROMATOGRAPHY
Chromatography is used to separate and analyse small amounts of mixtures
Methods involve a stationary phase (stays where it is)
and a mobile phase (moves)
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
gas liquid (glc) solid or liquid gas
However, they all work in the same way
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7. PAPER CHROMATOGRAPHY
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8. PAPER CHROMATOGRAPHY Stationary phase chromatography paper
Mobile phase suitable solvent (water, ethanol, organic solvent)
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9. 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.
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10. 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.
Uses Separating the colours in Smarties®
Separating the colours in, and identifying, inks
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11. 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.
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12. 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.
SOLVENT FRONT
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.
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13. 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.
SOLVENT FRONT
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
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14. 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
SOLVENT FRONT X Y
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15. 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
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16. GAS LIQUID CHROMATOGRAPHY (GLC)
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17. GAS LIQUID CHROMATOGRAPHY (GLC)
Stationary phase liquid adsorbed onto a solid support material
Mobile phase gas
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18. GAS LIQUID CHROMATOGRAPHY (GLC)
Stationary phase liquid adsorbed onto a solid support material
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
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19. GAS LIQUID CHROMATOGRAPHY (GLC)
Stationary phase liquid adsorbed onto a solid support material
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
• the column contains a liquid stationary phase, adsorbed on 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.
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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.
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21. 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
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22. 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
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23. 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
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24. 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.
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25. GAS CHROMATOGRAPHY – MASS SPECTROMETRY (GCMS)
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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
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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
Mass spectrometers were first used to identify the
presence of different isotopes.
Today, they are mainly used to work out relative molecular (formula) mass and identify unknown molecules.
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28. GAS CHROMATOGRAPHY – MASS SPECTROMETRY (GCMS)
Process When a peak is detected in gas chromatography, some of
the component is sent to a mass spectrometer
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29. 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...
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30. 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...
ANALYSER
DETECTOR
IONISER
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31. 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
ANALYSER
DETECTOR
IONISER
PARTICLES MUST BE IONISED SO THEY CAN BE ACCELERATED AND DEFLECTED
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32. 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
DETECTOR
IONISER
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33. 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 (heavier) = smaller deflection
ANALYSER
DETECTOR
IONISER
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34. 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 (heavier) = 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
IONISER
ANALYSER
DETECTOR
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35. 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 (heavier) = 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
ANALYSER
DETECTOR
IONISER
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36. MASS SPECTROMETRY - FRAGMENTATION
Mass spectrometry is used to identify unknown or new compounds.
The mass spectra of compounds are much more complicated than that of atoms because of fragmentation.
When a molecule is ionised it forms a MOLECULAR ION which can undergo FRAGMENTATION or RE-ARRANGEMENT to produce particles of smaller mass.
Only particles with a positive charge will be deflected and detected.
The resulting spectrum has many peaks.
The final peak shows the molecular ion and indicates the molecular mass. The rest of the spectrum provides information about the structure.
IONISATION
MOLECULAR ION
FRAGMENTION
RE-ARRANGEMENT
FRAGMENTION
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37. QUESTIONS
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38. MASS SPECTRUM OF AN ORGANIC COMPOUND
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39. MASS SPECTRUM OF AN ORGANIC COMPOUND
Which signal is caused by the molecular ion?
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40. MASS SPECTRUM OF AN ORGANIC COMPOUND
The final signal in the spectrum is that of the molecular ion.
Which signal is caused by the molecular ion?
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41. MASS SPECTRUM OF AN ORGANIC COMPOUND
What is the relative molecular (formula) mass of the compound?
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42. 58 MASS SPECTRUM OF AN ORGANIC COMPOUND
What is the relative molecular (formula) mass of the compound?
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43. MASS SPECTRUM OF AN ORGANIC COMPOUND
If the compound is a hydrocarbon, what is its molecular formula?
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44. C4H10 MASS SPECTRUM OF AN ORGANIC COMPOUND
What is the relative molecular (formula) mass of the compound?
C4H10
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45. ©2011 JONATHAN HOPTON & KNOCKHARDY PUBLISHING
ANALYSING SUBSTANCES
THE END
©2011 JONATHAN HOPTON & KNOCKHARDY PUBLISHING