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Chemistry > 3.16 chromatography > Flashcards

3.16 chromatography Flashcards

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
TLC experimental details: dissolve a small sample of mixture in
solvent
26
TLC experimental details: draw a ... a short distance from the bottom of the TLC plate
pencil line
27
TLC experimental details: place a spot of... on the pencil line and allow to dry
component
28
TLC experimental details: place the TLC plate in a beaker containing a small amount of
the solvent
29
TLC experimental details: cover beaker with
a lid
30
TLC experimental details: allow solvent to rise up tlc plate and stop before
it reaches the top
31
TLC experimental details: mark on the ... in ... once the solvent has risen almost to the top of the TLC plate
solvent front in pencil
32
TLC experimental details: what can be used to make the compounds visible
locating agent
33
TLC: locating agents
uv light, ninhydrin, I2 crystals, MnO4
34
TLC: advantages compared to paper chromatography
- faster - requires smaller amounts of mixtures - better resolution
35
TLC: limitations
- 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
Rf
distance moved by spot/distance moved by solvent
37
Rf values can only be between
0 and 1
38
CC: uses
separating large amounts of mixtures
39
CC: moving phase
liquid solvent which passes down and out of column (eluent)
40
CC: stationary phase
solid beads
41
CC experimental details: fill a glass tube with
stationary phase, held in place by a filter or mineral wool plug
42
CC experimental details: cover all powder in
solvent
43
CC experimental details: dissolve mixture to be sampled in
minimum amount of solvent
44
CC experimental details: place mixture on top of
solid phase
45
CC experimental details: run mixture through column by
opening tap and adding solvent at the top
46
CC experimental details: time taken for each component to reach end of column recorded, this is known as
retention time
47
CC: advantages
-used for larger amounts of sample
48
GC: what kind of method is GC
a very sensitive quantitative method
49
GC: uses
to test a wide range of compounds
50
GC: moving phase
inert carrier gas at high temp and pressure
51
GC: stationary phase
thin layer of solid/liquid- both in capillary tube
52
GC experimental details: mixture injected into gas chromatograph where it
vapourises
53
GC experimental details: what flushes mixture through the column
the carrier gas (moving phase)
54
GC experimental details: why do the components slow down
as they interact with the stationary phase
55
GC experimental details: each component leaves the column at a different time and is
detected
56
retention time
the time taken for a component to pass from the column inlet to the detector
57
correlation between retention time and components solubility in stationary phase
the longer the retention time, the greater the components solubility in the stationary phase
58
why can retention times be theoretically used for identification
different compounds have different retention time values
59
gas chromatogram: number of peaks=
number of components in the mixture
60
gas chromatogram: area under each peak proportional to
amount of a component in the mixture
61
limitations of GC:
- 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
what does GCMS stand for
gas chromatography mass spectrometry
63
what does combining gas chromatography with mass spectrometry give
a far more powerful tool than gas chromatography alone
64
what is gas chromatography not good at despite being used to separate components
identifying structure
65
GCMS: what is mass spectrometry used to do
identify the separated components
66
GCMS: first stage
GC first used to separate components in the mixture
67
GCMS: second stage
each separated compoentns directed to MS in turn
68
GCMS: third stage
each mass spectrum can be analysed/compared with spectral database, so enabling compound to be identified
69
GCMS: fourth stage
quantity of each component can also be determined
70
what is a mass specturm
a plot of relative abundance against mass to charge ratio
71
what does a mass spectrum consist of
a series of peaks at different masses corresponding to the mass of the whole molecule and the masses of the fragment ions
72
what will the peak with the highest m/z ratio in a mass spectrum be down to
the molecular ion
73
what does fragmentation provide in mass spectrums
structural detail
74
uses of GCMS
- forensic and drug analysis - environmental analysis - airport security - space probes

Chemistry (42 decks)

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