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A-level Chemistry > CbD - Gas-liquid chromatography > Flashcards

CbD - Gas-liquid chromatography Flashcards

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1
Q

What is gas-liquid chromatography good for?

A

Separating and identifying components.

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2
Q

What is chromatography used for?

A

To separate stuff in a mixture.

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3
Q

What can you do once stuff has been separated out in a mixture using chromatography?

A

Identify the components.

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4
Q

What are the symbols/shorthand way for writing gas-liquid chromatography?

A

GLC

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5
Q

What are the 2 phases in chromatography?

A

A mobile phase

A stationary phase

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6
Q

How many phases are there in chromatography?

A

2

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7
Q

What is a mobile phase?

A

Where the molecules can move. This is always a liquid or a gas.

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8
Q

What state is the mobile phase always in in chromatography?

A

Liquid or gas.

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9
Q

What is a stationary phase?

A

Where molecules can’t move. This must be a solid, or a liquid on a solid support.

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10
Q

What state must the stationary phase be in in chromatography?

A

This must be a solid, or a liquid on a solid support.

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11
Q

What is the relationship between the mobile and stationary phase in chromatography?

A

The mobile phase moves through the stationary phase.

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12
Q

What happens as the mobile phase moves through the stationary phase?

A

The components in the mixture separate out between the phases.

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13
Q

What are gas-liquid chromatograms great for showing?

A

The proportion of esters in oils used as binding mediums in paint.

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14
Q

Because gas-liquid chromatograms are great for showing the proportion of esters in oils used as binding mediums in paint, what does this help to do?

A

Identify the oil present.

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15
Q

Why are gas-liquid chromatograms great for showing the proportion of esters in oils used as binding mediums in paint?

A

Only a very small sample of paint is needed.

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16
Q

What is the stationary phase in GLC?

A

A solid, or a viscous, high boiling point liquid (such as an oil), which coats a porous support inside a long tube.

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17
Q

What is the tube with the stationary phase like in GLC?

A

Coiled to save space, and built into an oven.

18
Q

What is the tube also known as in GLC?

A

A column (even though it is coiled).

19
Q

What is the mobile phase in GLC?

A

An inert (unreactive) carrier gas such as nitrogen or helium.

20
Q

How do you carry out GLC?

A
  • The sample to be analysed is injected into the stream of carrier has, which carries it through the tube and over the stationary phase.
  • The components of the mixture constantly dissolve in the stationary phase, evaporate into the mobile phase and then redissolve as they travel through the tube.
21
Q

What happens to the components of the mixture as GLC is happening?

A

The components of the mixture constantly dissolve in the stationary phase, evaporate into the mobile phase and then redissolve as they travel through the tube.

22
Q

What does the solubility of each component in the mixture determine?

A

How long it spends dissolved in the stationary phase and how long it spends moving along the tube in the mobile phase.

23
Q

What about each component in the mixture determines how long it spends dissolved in the stationary phase and how long it spends moving along the tube in the mobile phase?

A

The solubility of each component in the mixture.

24
Q

Explain how substances with a high solubility will spend their time in GLC

A

They will spend more time dissolved, so will take longer to travel through the tube to the detector than one with a lower solubility.

25
Q

Which level of solubility would substances that spend more time dissolved, so will take longer to travel through the tube to the detector have?

A

A higher solubility.

26
Q

What do GLC chromatograms show?

A

The proportions of the components in a mixture.

27
Q

What does a GLC chromatogram look like?

A

A series of peaks at the times when the detector senses something other than the carrier gas leaving the tube.

28
Q

What can the peaks on a chromatogram be used for?

A

To identify the substances within a sample and their relative proportions.

29
Q

What is the time taken to reach the detector in GLC called?

A

The retention time.

30
Q

What is the retention time in GLC?

A

The time taken to reach the detector.

31
Q

What does each peak on a chromatogram correspond to?

A

A substance with a particular retention time.

32
Q

How are retention times measured?

A

From zero (in time) to the centre of each peak.

33
Q

Where can you use retention times/what are they useful for?

A

They can be looked up in a reference table to identify the substances present.

34
Q

What has to be the same when you look up retention times in a reference table to identify substances present?

A

The conditions of the test and reference table are the same.

35
Q

What can you look up in a reference table to identify the substances present from GLC?

A

Retention times.

36
Q

What do you have to be careful about when identifying substances from retention times?

A

Similar compounds often have similar retention times, so they’re difficult to identify accurately.

37
Q

What is the area under each peak on GLC chromatograms proportional to?

A

The relative amount of each substance in the original mixture.

38
Q

What are the axis on a GLC chromatogram?

A

X-axis = Time/min

Y-axis = Recorder response

39
Q

What can GLC be combined with?

A

Mass spectrometry

40
Q

Why is it good pairing GLC and mass spectrometry?

A

GLC is very good at separating a mixture into its individual components, but not so good at identifying those components.

Mass spectrometry, however, is great at identifying unknown compounds, but would give confusing results from a mixture of substances.

So putting these two techniques together gives an extremely useful analytical tool.

41
Q

What is gas-liquid chromatography-mass spectrometry (GLC-MS)?

A

Combines the benefits of GLC and MS to make a super analysis tool.

42
Q

How is GLC-MS used/how is it carried out?

A

A sample is separated using GLC, but instead of going to a detector, the separated components are fed into a mass spectrometer. The spectrometer produces a mass spectrum for each component, which can be used to identify each one and show what the original sample consisted of.

A-level Chemistry (51 decks)

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