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Chemistry > 3.16 chromatography > Flashcards

3.16 chromatography Flashcards

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1
Q

all forms of chromatography involve the distribution of the components of a mixture between which 2 phases

A

a stationary phase and a moving phase

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2
Q

phase

A

a state such as solid, liquid or gas

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3
Q

what does the mobile phase pass over

A

the stationary phase

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4
Q

what doesn’t the stationary phase do

A

move

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5
Q

adsoprtion

A

the process by which a sold holds molecules onto its surface

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6
Q

what does TLC stand for

A

thin layer chromatography

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7
Q

what does cc stand for

A

column chromatography

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8
Q

what does GC stand for

A

gas chromatography

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9
Q

TLC: stationary phase

A

piece of card/filter paper

TLC plate- silica/alumina coating
glass

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10
Q

TLC: mobile phase

A

various solvents used

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11
Q

CC: stationary phase

A

glass column packed with a solid

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12
Q

CC: mobile phase

A

a liquid solvent (eluent) moves down the column

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13
Q

GC: stationary phase

A

solid/solid coated with lqiuid packed into a capillary tube

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14
Q

TLC: mobile phase

A

unreactive carrier gas (eg He/N2) used under pressure at high temp

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15
Q

separation of components: how does separation occur if the stationary phase is a solid

A

adsorption

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16
Q

separation of components: what is the correlation between strength of adsorption and speed of component moving through mobile phase

A

the stronger the adsorption to the stationary solid phase, the slower the component moves through the mobile phase

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17
Q

separation of components: how does separation occur if the stationary phase is a liquid

A

by relative solubility

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18
Q

separation of components: what is the correlation between solubility of liquid stationary phase and speed of component moving through mobile phase

A

the greater the solubility in the stationary liquid phase, the slower the component moves through the mobile phase

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19
Q

separation of components: what is the rate of movement of a component recorded as and what can this be used to idetify

A

recorded as Rf value/retention time

can be used to identify a component

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20
Q

separation of components: what properties is the strength of adsorption and relative solubility of a molecule affected by

A

-charge
-polarity
stereoisomerism

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21
Q

separation of components: what does separation depend of the balance between

A

solubility in the moving phase and retention in the stationary phase

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22
Q

TLC: uses

A

separation- identifying components in mixtures

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23
Q

TLC: moving phase

A

solvent

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24
Q

TLC: stationary phase

A

TLC plate

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25
Q

TLC experimental details: dissolve a small sample of mixture in

A

solvent

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26
Q

TLC experimental details: draw a … a short distance from the bottom of the TLC plate

A

pencil line

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27
Q

TLC experimental details: place a spot of… on the pencil line and allow to dry

A

component

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28
Q

TLC experimental details: place the TLC plate in a beaker containing a small amount of

A

the solvent

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29
Q

TLC experimental details: cover beaker with

A

a lid

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30
Q

TLC experimental details: allow solvent to rise up tlc plate and stop before

A

it reaches the top

31
Q

TLC experimental details: mark on the … in … once the solvent has risen almost to the top of the TLC plate

A

solvent front in pencil

32
Q

TLC experimental details: what can be used to make the compounds visible

A

locating agent

33
Q

TLC: locating agents

A

uv light, ninhydrin, I2 crystals, MnO4

34
Q

TLC: advantages compared to paper chromatography

A
  • faster
  • requires smaller amounts of mixtures
  • better resolution
35
Q

TLC: limitations

A
  • similar compounds have similar Rf values
  • unknown compounds have no Rf values for reference
  • can be difficult to find a solvent to separate all components in a mixture
36
Q

Rf

A

distance moved by spot/distance moved by solvent

37
Q

Rf values can only be between

A

0 and 1

38
Q

CC: uses

A

separating large amounts of mixtures

39
Q

CC: moving phase

A

liquid solvent which passes down and out of column (eluent)

40
Q

CC: stationary phase

A

solid beads

41
Q

CC experimental details: fill a glass tube with

A

stationary phase, held in place by a filter or mineral wool plug

42
Q

CC experimental details: cover all powder in

A

solvent

43
Q

CC experimental details: dissolve mixture to be sampled in

A

minimum amount of solvent

44
Q

CC experimental details: place mixture on top of

A

solid phase

45
Q

CC experimental details: run mixture through column by

A

opening tap and adding solvent at the top

46
Q

CC experimental details: time taken for each component to reach end of column recorded, this is known as

A

retention time

47
Q

CC: advantages

A

-used for larger amounts of sample

48
Q

GC: what kind of method is GC

A

a very sensitive quantitative method

49
Q

GC: uses

A

to test a wide range of compounds

50
Q

GC: moving phase

A

inert carrier gas at high temp and pressure

51
Q

GC: stationary phase

A

thin layer of solid/liquid- both in capillary tube

52
Q

GC experimental details: mixture injected into gas chromatograph where it

A

vapourises

53
Q

GC experimental details: what flushes mixture through the column

A

the carrier gas (moving phase)

54
Q

GC experimental details: why do the components slow down

A

as they interact with the stationary phase

55
Q

GC experimental details: each component leaves the column at a different time and is

A

detected

56
Q

retention time

A

the time taken for a component to pass from the column inlet to the detector

57
Q

correlation between retention time and components solubility in stationary phase

A

the longer the retention time, the greater the components solubility in the stationary phase

58
Q

why can retention times be theoretically used for identification

A

different compounds have different retention time values

59
Q

gas chromatogram: number of peaks=

A

number of components in the mixture

60
Q

gas chromatogram: area under each peak proportional to

A

amount of a component in the mixture

61
Q

limitations of GC:

A
  • many 1000s compounds have same retention time and peak shape
  • peaks for components present in high conc can hide smaller peaks with same retention time
  • unknowns have 0 reference
62
Q

what does GCMS stand for

A

gas chromatography mass spectrometry

63
Q

what does combining gas chromatography with mass spectrometry give

A

a far more powerful tool than gas chromatography alone

64
Q

what is gas chromatography not good at despite being used to separate components

A

identifying structure

65
Q

GCMS: what is mass spectrometry used to do

A

identify the separated components

66
Q

GCMS: first stage

A

GC first used to separate components in the mixture

67
Q

GCMS: second stage

A

each separated compoentns directed to MS in turn

68
Q

GCMS: third stage

A

each mass spectrum can be analysed/compared with spectral database, so enabling compound to be identified

69
Q

GCMS: fourth stage

A

quantity of each component can also be determined

70
Q

what is a mass specturm

A

a plot of relative abundance against mass to charge ratio

71
Q

what does a mass spectrum consist of

A

a series of peaks at different masses corresponding to the mass of the whole molecule and the masses of the fragment ions

72
Q

what will the peak with the highest m/z ratio in a mass spectrum be down to

A

the molecular ion

73
Q

what does fragmentation provide in mass spectrums

A

structural detail

74
Q

uses of GCMS

A
  • forensic and drug analysis
  • environmental analysis
  • airport security
  • space probes

Chemistry (42 decks)

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