CbD - Gas-liquid chromatography

Question 1

What is gas-liquid chromatography good for?

Answer 1

Separating and identifying components.

Question 2

What is chromatography used for?

Answer 2

To separate stuff in a mixture.

Question 3

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

Answer 3

Identify the components.

Question 4

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

Answer 4

GLC

Question 5

What are the 2 phases in chromatography?

Answer 5

A mobile phase

A stationary phase

Question 6

How many phases are there in chromatography?

Answer 6

2

Question 7

What is a mobile phase?

Answer 7

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

Question 8

What state is the mobile phase always in in chromatography?

Answer 8

Liquid or gas.

Question 9

What is a stationary phase?

Answer 9

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

Question 10

What state must the stationary phase be in in chromatography?

Answer 10

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

Question 11

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

Answer 11

The mobile phase moves through the stationary phase.

Question 12

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

Answer 12

The components in the mixture separate out between the phases.

Question 13

What are gas-liquid chromatograms great for showing?

Answer 13

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

Question 14

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?

Answer 14

Identify the oil present.

Question 15

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

Answer 15

Only a very small sample of paint is needed.

Question 16

What is the stationary phase in GLC?

Answer 16

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

Question 17

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

Answer 17

Coiled to save space, and built into an oven.

Question 18

What is the tube also known as in GLC?

Answer 18

A column (even though it is coiled).

Question 19

What is the mobile phase in GLC?

Answer 19

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

Question 20

How do you carry out GLC?

Answer 20

• 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.

Question 21

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

Answer 21

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.

Question 22

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

Answer 22

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

Question 23

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?

Answer 23

The solubility of each component in the mixture.

Question 24

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

Answer 24

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

Question 25

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

Answer 25

A higher solubility.

Question 26

What do GLC chromatograms show?

Answer 26

The proportions of the components in a mixture.

Question 27

What does a GLC chromatogram look like?

Answer 27

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

Question 28

What can the peaks on a chromatogram be used for?

Answer 28

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

Question 29

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

Answer 29

The retention time.

Question 30

What is the retention time in GLC?

Answer 30

The time taken to reach the detector.

Question 31

What does each peak on a chromatogram correspond to?

Answer 31

A substance with a particular retention time.

Question 32

How are retention times measured?

Answer 32

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

Question 33

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

Answer 33

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

Question 34

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

Answer 34

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

Question 35

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

Answer 35

Retention times.

Question 36

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

Answer 36

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

Question 37

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

Answer 37

The relative amount of each substance in the original mixture.

Question 38

What are the axis on a GLC chromatogram?

Answer 38

X-axis = Time/min Y-axis = Recorder response

Question 39

What can GLC be combined with?

Answer 39

Mass spectrometry

Question 40

Why is it good pairing GLC and mass spectrometry?

Answer 40

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.

Question 41

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

Answer 41

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

Question 42

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

Answer 42

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.