3.3.16 Chromatography Knowledge Flashcards
(61 cards)
1
Q
what is the stationary phase in chromatography?
A
solid substance
2
Q
what is the mobile phase in chromatography?
A
liquid or gas
3
Q
what is the purpose of the stationary phase in chromatography?
A
mixture passes over this in order to be separated
4
Q
what is the purpose of the mobile phase in chromatography?
A
carries mixture over the solid material
5
Q
how is a mixture separated in chromatography?
A
separation depends on the balance between solubility/affinity to the mobile phase and retention by the stationary phase
6
Q
when will a component travel slowly in chromatography?
A
- If a component has a low solubility in the mobile phase, it will travel slowly with the solvent
- If a component has a high affinity to the stationary phase, it will travel slowly
7
Q
when will a component travel quickly in chromatography?
A
- If a component has a low affinity to the stationary phase, it will travel quickly
- If a component is highly soluble in the mobile phase, it will travel along quickly with the solvent
8
Q
how do you ensure the mixture separates in chromatography?
A
by selecting a suitable combination of mobile and stationary phases
9
Q
describe the process of thin layer chromatograhy
A
- Stationary phase: a thin piece of aluminium/glass is coated in silica gel or aluminia AKA a TLC plate
- Samples of mixture are dropped on a line on the bottom of the TLC plate
- Mobile phase: TLC plate is suspended in a small amount of solvent/eluant which soaks up the plate.
- Once dry, plate is examined under UV light or developed using chemical agents to make the spots visible
- The number of spots gives the number of components present in the mixture
10
Q
what is the stationary phase in thin layer chromatography?
A
a thin piece of aluminium/glass is coated in silica gel or aluminia
11
Q
what is the plate in thin layer chromatography coated in?
A
silica gel or aluminia
12
Q
what is the plate in thin layer chromatography made of?
A
aluminium or glass
13
Q
what is the mobile phase in thin layer chromatography?
A
solvent or eluant
14
Q
how do you see the results of thin layer chromatography?
A
under UV light or developed using chemical agents
15
Q
what does the number of spots in thin layer chromatography indicate?
A
the number of components in the mixture
16
Q
what does it mean If a spot has travelled further up the TLC plate?
A
it is more soluble in the mobile phase and has a low affinity for the stationary phase
17
Q
what dies it mean If a spot has travelled less far up the TLC plate?
A
it is less soluble in the mobile phase and has a high affinity for the stationary phase
18
Q
what does Rf stand for?
A
retention factor
19
Q
how do you calculate an Rf value?
A
distance moved by component / distance moved by solvent front
20
Q
what does an Rf value show?
A
how far a component has moved compared to the solvent front
21
Q
what can Rf values be used to do?
A
Can be compared to those in a data book
22
Q
what are the advantages of thin layer chromatography?
A
- Faster than paper chromatography
- Will work on very small samples
- Can be used to determine when a chemical reaction is complete
23
Q
what are the disadvantages of thin layer chromatography?
A
- Similar compounds may have similar Rf values
- Conditions must be kept the same in order to fairly compare Rf values
- Unknown compounds have no reference Rf values
- It can be difficult to find a solvent which separates all components in a mixture
- Cannot be used to separate large quantities
24
Q
describe the process of column chromatography
A
- Column = narrow glass tube with a spout and tap
- Stationary phase = column packed with powder (silica or aluminia)
- Mixture is loaded onto the top of the column
- Mobile phase = solvent/eluant poured onto the top of the column and soaks down through the stationary phase
- Different components travel down at different rates; one will reach the bottom and can be collected into a beaker first and then so on.
25
what is the stationary phase in column chromatography?
column packed with powder (silica or aluminia)
26
what is the powder used in column chromatography?
silica or aluminia
27
what is the mobile phase in column chromatography?
solvent/eluant poured onto the top of the column
28
what is an advantage of column chromatography?
larger quantities can be separated
29
what is gas-liquid chromatography used for?
used to separate complex mixtures of volatile components
30
describe the process of gas-liquid chromatography
- Mobile phase = carrier gas, typically unreactive (nitrogen or helium)
- Carrier gas flows through a long and thin tube (~0.5mm diameter) - the capillary column - made of glass or metal. Temp can be varied.
- Stationary phase = thin coating of a liquid (e.g. high molecular mass alkane with a high boiling point) or solid (e.g. silicone polymers) on the inside of the column
- Sample is injected into the column and carrier gas transports components along the column at different rates, so they separate out.
- Mobile phase is not a solvent, so the components separate due to different affinity to the stationary phase, not solubility
31
what is the mobile phase in gas-liquid chromatography?
carrier gas, typically unreactive (nitrogen or helium)
32
what is usually the carrier gas in gas-liquid chromatography?
nitrogen or helium
33
what is the stationary phase in gas-liquid chromatography?
thin coating of a liquid (e.g. high molecular mass alkane with a high boiling point) or solid (e.g. silicone polymers) on the inside of the column
34
what is the capillary column in gas-liquid chromatography usually made of?
glass or metal
35
give an example of a liquid suitable for the stationary phase of gas-liquid chromatography
high molecular mass alkane with a high boiling point
36
give an example of a solid suitable for the stationary phase of gas-liquid chromatography
silicone polymer
37
why do components separate in gas-liquid chromatography?
Mobile phase is not a solvent, so the components separate due to different affinity to the stationary phase, not solubility
38
what is measured in gas-liquid chromatography?
retention time
39
what is retention time a measure of?
time it takes from the point of injection for the component to reach the detector
40
what happens when components reach the detector in gas-liquid chromatography?
When components reach the detector, an electrical signal is produced.
41
how can components be identified using gas-liquid chromatography?
Components can be identified by comparing their retention times with known compounds.
42
how can relative amounts of components in a mixture be determined using gas-liquid chromatography?
Area of a peak in a gas chromatogram is proportional to the amount of a component in a mixture; relative amounts of components in a mixture can be determined by comparing peak areas.
43
what is the Area of a peak in a gas chromatogram proportional to?
the amount of a component in a mixture
44
what are the disadvantages of gas-liquid chromatography?
- Potentially thousands of chemicals have similar retention times, peak shapes, and detector responses, so compounds cannot be positively identified
- Not all substances in a sample may separated and detected; peaks may be 'hidden' behind others
- Unknown compounds have no reference retention times
45
what is GC-MS?
Linking a gas chromatograph to a mass spectrometer
46
what can help resolve some of the issues with gas-liquid chromatography?
Linking a gas chromatograph to a mass spectrometer
47
why can Linking a gas chromatograph to a mass spectrometer produce more accurate results?
- GC can separate components in a mixture but cannot identify them conclusively
- MS cannot separate components in a mixture but can identify them
48
what are some uses of GC-MS?
- Forensics: minute particles at the scene of a crime can be identified to provide evidence
- Environmental analysis: can identify organic pollutants e.g. waste water, drinking water quality, pesticides in food
- Airport security: can detect traces of explosives in luggage and on people
- Space probes: can collect and analyse materials from atmospheres of other planets.
49
how is GC-MS used in forensics?
minute particles at the scene of a crime can be identified to provide evidence
50
how is GC-MS used in environmental analysis?
can identify organic pollutants e.g. waste water, drinking water quality, pesticides in food
51
how is GC-MS used in airport security?
can detect traces of explosives in luggage and on people
52
how is GC-MS used on space probes?
can collect and analyse materials from atmospheres of other planets.
53
what happens if a polar solvent is used in TLC?
- a more polar component will dissolve well in the solvent and travel further up the TLC plate.
- a less polar component will dissolve poorly in the solvent and travel less far up the TLC plate.
54
what happens if a non-polar solvent is used in TLC?
- a more polar component will dissolve poorly in the solvent and travel less far up the TLC plate.
- a less polar component will dissolve well in the solvent and travel further up the TLC plate.
55
What happens if a polar stationary phase is used in TLC?
- a more polar component with have more affinity to it and travel less far up the TLC plate.
- a less polar component with have less affinity to it and travel further up the TLC plate.
56
is silica polar or non-polar?
polar
57
what happens if a non-polar stationary phase is used in TLC?
- a more polar component with have less affinity to it and travel further up the TLC plate.
- a less polar component with have more affinity to it and travel less far up the TLC plate.
58
what happens if a polar solvent is used in CC?
- a more polar component will dissolve well in the solvent and be the first to be collected from the bottom of the column.
- a less polar component will dissolve poorly in the solvent and would take longer to be collected from the bottom of the column.
59
WHAT HAPPENS If a non-polar solvent is used in CC?
- a more polar component will dissolve poorly in the solvent and would take longer to be collected from the bottom of the column.
- a less polar component will dissolve well in the solvent and would be the first to be collected from the bottom of the column.
60
what happens if a polar stationary phase is used in CC?
- a more polar component will have a high affinity to it and would take longer to be collected from the bottom of the column.
- a less polar component will have a low affinity to it and would be the first to be collected from the bottom of the column.
61
what happens if a non-polar stationary phase is used in CC?
- a less polar component will have a high affinity to it and would take longer to be collected from the bottom of the column.
- a more polar component will have a low affinity to it and would be the first to be collected from the bottom of the column.
