Chromatography

Question 1

What are the components of the moving phase in TLC?

Answer 1

Solvent

The solvent carries the samples up the TLC plate.

Question 2

What is the stationary phase in TLC made of?

Answer 2

Silica gel or alumina on aluminum, glass, or plastic

The stationary phase interacts with the compounds being separated.

Question 3

What is the purpose of adding a fluorescent compound to the TLC plate?

Answer 3

To aid in visualisation under UV light

Question 4

Why should TLC plates be held by the edges?

Answer 4

To prevent contamination from hands

Question 5

Why must the solvent level be below the baseline in TLC?

Answer 5

So the sample spots don’t dissolve in the solvent

Question 6

What causes the solvent to rise in TLC?

Answer 6

Capillary action

Question 7

When should the TLC plate be removed from the chamber?

Answer 7

When the solvent front is ~1cm from the top

Question 8

How are spots visualized in TLC using UV light?

Answer 8

The fluorescent background glows and sample spots quench the glow

Question 9

What is another method to visualize TLC spots besides UV?

Answer 9

Using a stain or developing agent like ninhydrin

Question 10

What is Rf in chromatography?

Answer 10

The ratio of the distance moved by the compound to the distance moved by the solvent front

Question 11

How does polarity affect movement in TLC?

Answer 11

More polar compounds move slower; less polar move faster

Question 12

Can TLC be used for paper chromatography?

Answer 12

Yes

Question 13

What are common uses of Rf values?

Answer 13

Compound identification and monitoring reactions

Question 14

What is the apparatus called in chromatography?

Answer 14

Chromatograph

Question 15

What is the pattern of separated substances called?

Answer 15

Chromatogram

Question 16

What does retention time refer to?

Answer 16

Time a component stays in the column

Question 17

What is chromatography in general terms?

Answer 17

A technique for separating mixtures based on affinities to phases

Question 18

What is the moving phase in gas chromatography (GC)?

Answer 18

Carrier gas (e.g., He or N₂)

Question 19

What is the stationary phase in GC?

Answer 19

Non-volatile liquid film on inert powder in a coiled tube

Question 20

How is the sample introduced in GC?

Answer 20

Injected in vaporized form into the column

Question 21

What does longer retention time indicate in GC?

Answer 21

Stronger interaction with the stationary phase

Question 22

What affects retention time and resolution in GC?

Answer 22

Gas flow rate, column length, and operating temperature

Question 23

How does gas flow rate affect resolution in GC?

Answer 23

Higher flow rate = lower retention time = lower resolution

Question 24

How does column length affect resolution in GC?

Answer 24

Longer column = higher resolution

Question 25

How does temperature affect GC analysis?

Answer 25

Alters retention time and peak separation

Question 26

How are components detected in GC?

Answer 26

By detectors which produce a chromatogram with peaks

Question 27

What does the area under a peak in GC represent?

Answer 27

The quantity of that component

Question 28

What are key uses of gas chromatography?

Answer 28

Separation of volatile compounds, trace analysis, and structure identification

Question 29

What is GC-MS?

Answer 29

Gas chromatography-mass spectrometry

Question 30

What is the stationary phase in column chromatography?

Answer 30

Silica or alumina powder

Question 31

What is the moving phase in column chromatography?

Answer 31

Eluent (a pure solvent or mixture)

Question 32

What is the process of adding eluent to a column called?

Answer 32

Elution

Question 33

How is the column packed in column chromatography?

Answer 33

With finely divided silica or alumina

Question 34

What happens after adding the sample in column chromatography?

Answer 34

Solvent is added to wash the sample down the column

Question 35

How are fractions collected in column chromatography?

Answer 35

In test tubes at intervals

Question 36

How is TLC used in column chromatography?

Answer 36

To check the contents of fractions

Question 37

How are compounds recovered after separation in column chromatography?

Answer 37

Evaporating the solvent from combined fractions

Question 38

Which compounds travel slowest in column chromatography?

Answer 38

Most polar compounds

Question 39

Why do polar compounds move slower in column chromatography?

Answer 39

They adsorb more strongly to the stationary phase

Question 40

What is the advantage of column chromatography over TLC?

Answer 40

It can separate larger amounts of sample

Question 41

What is the purpose of chromatography in general?

Answer 41

To separate and identify components in a mixture

Question 42

What is a carrier gas?

Answer 42

An inert gas used to transport samples in gas chromatography

Question 43

What is capillary action?

Answer 43

The movement of liquid through a porous material due to intermolecular forces

Question 44

What is the mobile phase?

Answer 44

The phase that moves through the stationary phase and carries the components

Question 45

What does ‘eluent’ refer to?

Answer 45

The solvent used in column chromatography to carry compounds through the column

Question 46

Why is visualisation important in TLC?

Answer 46

To detect colorless compounds

Question 47

What causes different movement rates in chromatography?

Answer 47

Differences in compound polarity and interaction with the phases

Question 48

What does a peak on a chromatogram represent?

Answer 48

A specific compound in the sample

Question 49

Why use a lid in TLC chambers?

Answer 49

To saturate the chamber and prevent solvent evaporation

Question 50

Why use inert gases in GC?

Answer 50

They don’t react with the sample or stationary phase

Question 51

Why do amino acids separate on a TLC plate

Answer 51

Difference in the balance between solubility in the mobile phase and attraction to the stationary phase