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

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slide1

ANALYSING SUBSTANCES

A guide for GCSE students

2010 SPECIFICATIONS

KNOCKHARDY PUBLISHING

slide2

HOPTON

ANALYSING SUBSTANCES

INTRODUCTION

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...

www.knockhardy.org.uk

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.

slide3

HOPTON

ANALYSING SUBSTANCES

  • CONTENTS
  • What is chromatography?
  • Paper chromatography
  • Gas liquid chromatography
  • Mass spectrometry
  • Questions
slide4

HOPTON

CHROMATOGRAPHY

Chromatography is used to separate and analyse small amounts of mixtures

slide5

HOPTON

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

slide6

HOPTON

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

slide7

HOPTON

PAPER CHROMATOGRAPHY

slide8

HOPTON

PAPER CHROMATOGRAPHY

Stationary phase chromatography paper

Mobile phase suitable solvent (water, ethanol, organic solvent)

slide9

HOPTON

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.

slide10

HOPTON

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

slide11

HOPTON

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.

slide12

HOPTON

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.

slide13

HOPTON

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

slide14

HOPTON

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

slide15

HOPTON

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

slide16

HOPTON

GAS LIQUID CHROMATOGRAPHY (GLC)

slide17

HOPTON

GAS LIQUID CHROMATOGRAPHY (GLC)

Stationary phase liquid adsorbed onto a solid support material

Mobile phase gas

slide18

HOPTON

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

slide19

HOPTON

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.

slide20

HOPTON

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.

slide21

HOPTON

GAS LIQUID CHROMATOGRAPHY (GLC)

Retention timeThe 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

slide22

HOPTON

GAS LIQUID CHROMATOGRAPHY (GLC)

Retention timeThe 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

slide23

HOPTON

GAS LIQUID CHROMATOGRAPHY (GLC)

Retention timeThe 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

slide24

HOPTON

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.

slide25

HOPTON

GAS CHROMATOGRAPHY – MASS SPECTROMETRY (GCMS)

slide26

HOPTON

GAS CHROMATOGRAPHY – MASS SPECTROMETRY (GCMS)

Process When a peak is detected in gas chromatography, some of

the component is sent to a mass spectrometer

slide27

HOPTON

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.

slide28

HOPTON

GAS CHROMATOGRAPHY – MASS SPECTROMETRY (GCMS)

Process When a peak is detected in gas chromatography, some of

the component is sent to a mass spectrometer

slide29

HOPTON

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...

slide30

HOPTON

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

slide31

HOPTON

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

slide32

HOPTON

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

slide33

HOPTON

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

slide34

ANALYSER

DETECTOR

IONISER

HOPTON

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

slide35

HOPTON

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

slide36

HOPTON

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

slide37

HOPTON

QUESTIONS

slide38

HOPTON

MASS SPECTRUM OF AN ORGANIC COMPOUND

slide39

HOPTON

MASS SPECTRUM OF AN ORGANIC COMPOUND

Which signal is caused by the molecular ion?

slide40

HOPTON

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?

slide41

HOPTON

MASS SPECTRUM OF AN ORGANIC COMPOUND

What is the relative molecular (formula) mass of the compound?

slide42

HOPTON

MASS SPECTRUM OF AN ORGANIC COMPOUND

58

What is the relative molecular (formula) mass of the compound?

slide43

HOPTON

MASS SPECTRUM OF AN ORGANIC COMPOUND

If the compound is a hydrocarbon, what is its molecular formula?

slide44

HOPTON

MASS SPECTRUM OF AN ORGANIC COMPOUND

What is the relative molecular (formula) mass of the compound?

C4H10

slide45

ANALYSING SUBSTANCES

THE END

©2011 JONATHAN HOPTON & KNOCKHARDY PUBLISHING