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MEHC U2 > Chromatography > Flashcards

Chromatography Flashcards

1
Q

What is chromatography?

A

Chromatography is the identification and the separation of mixtures of substances into their components

Also the concentration of each substance in a mixture

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2
Q

What is the same principle all forms of chromatography work on?

A

They all have a stationary phase (a solid, or a liquid supported on a solid) and a mobile phase (a liquid or a gas).

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3
Q

What does the stationary and mobile phase do?

A

The mobile phase flows through the stationary phase and carries the components of the mixture with it.

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4
Q

What happens to these two phases in Paper chromatography?

A

The stationary phase is a very uniform absorbent paper. The mobile phase is a suitable liquid solvent or mixture of solvents.

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5
Q

What are Rf values

A

The distance travelled relative to the solvent is a constant for a particular compound as long as you keep everything else constant - the type of paper and the exact composition of the solvent, for example.

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6
Q

What is the Rf value formula?

A

Distance travelled by compound / distance travelled by solvent

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7
Q

What are the 4 different types of chromatography?

A

Paper (PC), Thin-Layer (TLC), Gas-Liquid (GLC) and High Performance Liquid (HPLC).

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8
Q

What do types of chromatography rely on?

A

All the different types of chromatography rely on the equilibrium established when a compound distributes itself between two phases; one mobile and the other stationary.

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9
Q

What is paper chromatography?

A

In paper chromatography, we have already seen that the stationary phase
is a uniform adsorbent paper.

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10
Q

What is Thin-Layer Chromatography (TLC)?

A

In thin layer chromatography, the stationary phase is the solid support
material (often the plastic chromatography plate). The mobile phase is the
solvent that rises up the plate.

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11
Q

What are the 7 steps of gas-liquid chromatography?

A 
Injected 
Carried
Distribution 
Dissolve 
Volatile 
Detector
Chromatogram
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12
Q

What is the first step of the process of gas-liquid chromatography?

A

The sample to be reacted is injected into the gas stream just before it
enters the column

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13
Q

What is the second step of the process of gas-liquid chromatography?

A

The components of the mixture are then carried through the column in a
stream of gas

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14
Q

What is the third step of the process of gas-liquid chromatography?

A

Each compound distributes itself between the phases to different extents
and therefore emerges from the column at a different time.

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15
Q

What is the fourth step of the process of gas-liquid chromatography?

A

Some of the compounds dissolve in the stationary solvents more readily
than others; these travel through the column slower and so emerge last.

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16
Q

What is the fifth step of the process of gas-liquid chromatography?

A

The most volatile compounds usually emerge first.

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17
Q

What is the sixth step of the process of gas-liquid chromatography?

A

A detector on the outlet tube monitors compounds emerging from the
column.

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18
Q

What is the seventh step of the process of gas-liquid chromatography?

A

Signals from the detector are plotted out by a recorder as a

chromatogram.

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19
Q

What is a chromatogram?

A

The chromatogram shows the recorder response against the time which
has elapsed since the sample was injected into the column.
Each component of the mixture gives rise to a peak on the chromatogram.

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20
Q

State what would happen if the components in the mixture where not soluble in the mobile phase solvent.

A

They would not be attracted to the molecules in the mobile phase and therefore not seperate and move to different height up the stationary phase

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21
Q

It was found that component A travelled further up the stationary phase than component B. Explain what this indicates about the intermolecular interactions between these two components and the stationary phase.

A

Molecules in component B have greater attraction for molecules in the stationary phase and do not move as far in the same time period

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22
Q

What is the name of the process by which the solvent was drawn up the chromatography paper?

A

Capillary action

23
Q

What does Rf stand for?

A

Retardation factor

24
Q

What are 5 factors that affect the difference of the absorbance of the substances

A

different types of polar groups

the amount of charge polar chemical groups present

molecular weight

geometry

positions and number of c-c double bonds

25
What does it mean to have a Rf=0?
A substance does not migrate from the sample origin
26
What does it mean to have a Rf=1?
That it is not absorbed at all (migrated with the front)
27
What does the separation of individual components from a mixture rely on?
their differing solubility (due to differing intermolecular forces) in the moving liquid phase compared to the tendency to absorb to the stationary solid phase
28
How does seperation occur in paper chromatography?
due to differing polarity Very polar components have a strong tendency to absorb
29
What is the mobile phase for Paper chromatography?
By capillary action, the solvent chosen for the mixture to dissolve in and helps the substances absorb onto the chromatography paper
30
What is the stationary stage for paper chromatography?
A drop or two of this mixture is spotted along the pencil line drawn at one end of the strip of chromatography paper.
31
What is the stationary phase in column chromatography?
Glass tube packed with small beads of silica gel or alumina
32
What is the mobile phase in column chromatography?
The glass tube is filled with a solvent and a small volume of mixture is added to the top
33
How does separation occur in column chromatography?
Seperate bands are due to their different tendencies to absorb to the stationary phase or remain dissolved in the mobile phase
34
What is the stationary phase for thin layer chromatography?
Thin glass plate coated with either finely powdered alumina or silica (both polar in nature)
35
What is the mobile phase for thin layer chromatography?
Solvent chosen for its ability to dissolve and seperate the components in a mixture. Most components are molecular in nature, their polarity will affect their solubility in the solvent
36
What is gas chromatography?
Ideal for identifying individual substances and their concentration in a variety of complex mixtures For small organic molecules that can withstand relatively high temperatures. Requires compounds to be in a gas or vapour state
37
What is the mobile phase for gas chromatography?
Inert carrier gas eg. Helium or nitrogen
38
What is the stationary phase for gas chromatography?
High boiling point non-volatile viscous liquid that is coated onto solid particles such as silica
39
How does separation occur for gas chromatography?
The analyses volatility (tendency to evaporate). Analyses with a high volatility (Low boiling point analyses and weak intermolecular forces) have a greater tendency to remain in the mobile gas phase and tend to remain in the carrier gas, these quickly exit the column and hence have a lower retention time than high boiling point analyses
40
How does temperature of the column effect retention time for gas chromatography?
The higher the temperature, the lower the retention time
41
What is High Performance liquid chromatography?
Separation of larger organic molecular, substances that are unstable to heat Providing analytes are soluble in a suitable solvent and polarity allows
42
What is the mobile phase for HPLC?
Liquid solvent
43
What is the stationary phase for HPLC?
Tightly packed column of fine particles (SiO2)
44
Why is the size of the tightly pack column of fine particles important in HPLC?
Allows greater interaction with analyses in mobile phase Effect of greatly reducing the flow rate
45
Explain a normal phase for separation, relating to polarity.
In the Normal phase, the surface of the stationary solid phase is polar Eg. SiO2 Mobile phase is a non-polar or moderately polar solvent Eg. Hexane
46
How does polarity affect retention time in HPLC?
Configuration of polarities causes polar analysts to have greater retention time Higher the polarity of an analyse the greater the retention time will be. (Longer time it takes to travel through the column) The analyte will tend to dissolve in the phase of similar polarity. Thus if the stationary phase polarity closely matches the analyte's polarity then it's retention time will be great as it will tend to remain dissolved in the stationary phase. Conversely if the mobile phase polarity more closely matches the analytes polarity then it's retention time will be small as analyte tend to spend more time dissolved in the mobile phase.
47
Explain a reverse phase for separation, relating to polarity.
Stationary phase is non-polar Mobile is polar Most polar analyte elutes from the column first
48
What are three applications of GC?
Blood alcohol content Environmental monitoring of pollutants in the air, water and soil Testing for illegal or banned drugs in athletes
49
What are three applications of HPLC?
Analysis of amino acids, peptides, proteins in biochemical research Drug analysis and quality control in the development Quality control and analysis of fats and oils in food and beverage industry
50
For paper chromatography what is found at the bottom of the paper and the top, if the stationary phase is polar (paper or silica gel) and the mobile phase is moderately polar or non-polar substance?
Least polar at the top Most polar at the bottom As more polar substances have the tendency to absorb onto the paper (polar). These progress slowly up the strip. Compared to components that are less polar, which continue to quickly progress up to the top.
51
What happens if both the stationary and mobile stages are polar?
Components don't know where to go
52
What factors affect the retention time of an analyte in GC?
Volatility: the more volatile the analyte (lower boiling point) the more likely it will be in the vapour phase and hence the lower retention time Column temperature: the higher this is, the more likely the analyte is present as a vapour and hence present in the mobile gas phase. This retention time decreases with increasing column temperature Carrier gas flow rate: the greater this is, the shorter the retention time for all analytes
53
Why can't high molar mass substances like enzymes or blood proteins be spudded in GC for analysis?
GC is only suitable for analysing substances that are easily vaporised and do not decompose when heated sufficiently to make them vaporise. Enzymes and blood proteins have high molar masses and hence unlikely to be volatile and if heated will be broken down chemically. For this reason GC is not suited to their analysis. HPLC can be used instead as it does not rely on vaporising the compound. The compounds only needed to be prepared as solution.

MEHC U2 (8 decks)

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