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CHY1402 - Analytical methods and applications > Analytical chromatography > Flashcards

Analytical chromatography Flashcards

1
Q

What is chromatography?

A

Components of a mixture being distributed between 2 phases

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2
Q

What are the two phases?

A

Stationary

Mobile

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3
Q

What phase is the stationary phase?

A

Usually solid

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4
Q

What phase is the mobile phase?

A

Liquid or gas

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5
Q

What is a 2D layer of a stationary phase used for mostly?

A

Analytical

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6
Q

What is a 3D layer of a stationary phase used for?

A

Preparative

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7
Q

What are the 4 types of chromatography looked at?

A

Paper/thin layer
Column chromatography
HPLC
GC

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8
Q

What are the 4 principles of chromatography?

A
  • Separates them into their components
  • Stationary / mobile phase
  • Mobile phase carriers the mixture through the stationary phase
  • Different components travel at different rates/distances
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9
Q

On TLC, where does the solvent level need to be?

A

Below the sample spot

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10
Q

What do you need to draw the sample line on with and why?

A

Pencil

Does not run and mix with the sample

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11
Q

What is the solvent front?

A

The maximum distance the solvent travels up the TLC plate

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12
Q

What is overloading?

A

The sample is too concentrated and results in streaking and/or run together

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13
Q

Why does the lid need to be on the beaker for TLC?

A

The atmosphere will become saturated with a solvent vapour

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14
Q

Where does the solvent level need to be?

A

Just below the spot

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15
Q

What is the capillary force?

A

Upward movement

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16
Q

What is the equilibrium like when you run the TLC?

A

Goes from liquid to gas

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17
Q

What is the retention factor?

A

The numberical figure measuring the migration of a spot relative to the solvent front

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18
Q

When must you mark the solvent front?

A

Immediately before the solvent evaporates

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19
Q

What is the equation for working out the Rf values?

A

Rf = Distance travelled by the component / distance travelled by the solvent front

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20
Q

What is the Rf value not proof of?

A

Presence of a compound

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21
Q

What variables is the Rf value susceptible to?

A
  • Differences in solvent composition
  • The solid phase
  • Temperature
  • Size of the tank
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22
Q

When is an Rf value used?

A

As an aid for identification if there are identical conditions that are used

23
Q

What happens if the loading is too high?

A

There may be smearing/streaking

24
Q

What happens if the loading is too low?

A

Hard to visualise

25
Q

Wha is the mixed spot technique?

A

Plot the starting material first, then the mixed spot centre and the product mixture last

26
Q

What is the rate of migration?

A

Distribution of molecules between the mobile and stationary phase

27
Q

What factors affect migration?

A

Stationary phase
Mobile phase
Forces between the compound and the phases
Temperature

28
Q

What is the stationary phase?

A

Solid phase/adsorbent

29
Q

What are the two common adsorbents?

A

Silica gel

Alumina gel

30
Q

What two things are important when you look at the stationary phase?

A

The particle size and homogeneity

31
Q

What type of structure does silica gel have?

A

Extended covalent structure

32
Q

What is the surface of silica gel like?

A

Si-OH

Very polar

33
Q

How does the silica gel interact with the TLC plate?

A

The polar OH groups interact with the compounds on the TLC plate

34
Q

How does the substance move when there is a strong interaction with the stationary phase?

A

Moves slowly

35
Q

How does the substance move when there is a weak interaction with the stationary phase?

A

Moves quickly

36
Q

What type of Rf value does a polar compound have?

A

Small Rf

37
Q

What type of Rf value does a non polar compound have?

A

Large Rf

38
Q

How are polar molecules held on the solid phase?

A

By dipole-dipole interactions with the polar groups on the solid phase surface

39
Q

Why do non-polar compounds pass more quickly up the TLC plate?

A

There are no dipole-dipole interactions

40
Q

What happens in the mobile phase?

A

Solvent dissolves the mixture

Compounds carried up the plate

41
Q

What does the mobile phase need to be like to move an apolar compound?

A

Needs to be flexible

42
Q

What does the mobile phase need to be to move a polar compound?

A

Polar

43
Q

What does the mobile phase need to be to separate two components?

A

A balance between flexibility/polarity needs to be found

44
Q

What is crucial in the mobile phase?

A

Choice of eluent

45
Q

What is the order of solvents from slowest on SiO2 to fastest on SiO2?

A 
Hexane 
Toluene 
DCM 
Diethyl ether 
EtOAc 
MeCN 
THF 
iPrOH 
MeOH 
H2O
46
Q

What is the relative polarity of hexane on SiO2?

A

0.01

47
Q

What is the relative polarity of toluene on SiO2?

A

0.22

48
Q

What is the relative polarity of DCM on SiO2?

A

0.30

49
Q

What is the relative polarity of diethyl ether on SiO2?

A

0.43

50
Q

What is the relative polarity of EtOAc on SiO2?

A

0.48

51
Q

What is the relative polarity of MeCN on SiO2?

A

0.52

52
Q

What is the relative polarity of iPrOH on SiO2?

A

0.60

53
Q

What is the relative polarity of H2O on SiO2?

A

> > 1

54
Q

What is the relative polarity of MeOH on SiO2?

A

0.70

CHY1402 - Analytical methods and applications (14 decks)

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