Analytical chromatography

Question 1

What is chromatography?

Answer 1

Components of a mixture being distributed between 2 phases

Question 2

What are the two phases?

Answer 2

Stationary

Mobile

Question 3

What phase is the stationary phase?

Answer 3

Usually solid

Question 4

What phase is the mobile phase?

Answer 4

Liquid or gas

Question 5

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

Answer 5

Analytical

Question 6

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

Answer 6

Preparative

Question 7

What are the 4 types of chromatography looked at?

Answer 7

Paper/thin layer
Column chromatography
HPLC
GC

Question 8

What are the 4 principles of chromatography?

Answer 8

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

Question 9

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

Answer 9

Below the sample spot

Question 10

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

Answer 10

Pencil

Does not run and mix with the sample

Question 11

What is the solvent front?

Answer 11

The maximum distance the solvent travels up the TLC plate

Question 12

What is overloading?

Answer 12

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

Question 13

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

Answer 13

The atmosphere will become saturated with a solvent vapour

Question 14

Where does the solvent level need to be?

Answer 14

Just below the spot

Question 15

What is the capillary force?

Answer 15

Upward movement

Question 16

What is the equilibrium like when you run the TLC?

Answer 16

Goes from liquid to gas

Question 17

What is the retention factor?

Answer 17

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

Question 18

When must you mark the solvent front?

Answer 18

Immediately before the solvent evaporates

Question 19

What is the equation for working out the Rf values?

Answer 19

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

Question 20

What is the Rf value not proof of?

Answer 20

Presence of a compound

Question 21

What variables is the Rf value susceptible to?

Answer 21

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

Question 22

When is an Rf value used?

Answer 22

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

Question 23

What happens if the loading is too high?

Answer 23

There may be smearing/streaking

Question 24

What happens if the loading is too low?

Answer 24

Hard to visualise

Question 25

Wha is the mixed spot technique?

Answer 25

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

Question 26

What is the rate of migration?

Answer 26

Distribution of molecules between the mobile and stationary phase

Question 27

What factors affect migration?

Answer 27

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

Question 28

What is the stationary phase?

Answer 28

Solid phase/adsorbent

Question 29

What are the two common adsorbents?

Answer 29

Silica gel | Alumina gel

Question 30

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

Answer 30

The particle size and homogeneity

Question 31

What type of structure does silica gel have?

Answer 31

Extended covalent structure

Question 32

What is the surface of silica gel like?

Answer 32

Si-OH | Very polar

Question 33

How does the silica gel interact with the TLC plate?

Answer 33

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

Question 34

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

Answer 34

Moves slowly

Question 35

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

Answer 35

Moves quickly

Question 36

What type of Rf value does a polar compound have?

Answer 36

Small Rf

Question 37

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

Answer 37

Large Rf

Question 38

How are polar molecules held on the solid phase?

Answer 38

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

Question 39

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

Answer 39

There are no dipole-dipole interactions

Question 40

What happens in the mobile phase?

Answer 40

Solvent dissolves the mixture | Compounds carried up the plate

Question 41

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

Answer 41

Needs to be flexible

Question 42

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

Answer 42

Polar

Question 43

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

Answer 43

A balance between flexibility/polarity needs to be found

Question 44

What is crucial in the mobile phase?

Answer 44

Choice of eluent

Question 45

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

Answer 45

``` Hexane Toluene DCM Diethyl ether EtOAc MeCN THF iPrOH MeOH H2O ```

Question 46

What is the relative polarity of hexane on SiO2?

Answer 46

0.01

Question 47

What is the relative polarity of toluene on SiO2?

Answer 47

0.22

Question 48

What is the relative polarity of DCM on SiO2?

Answer 48

0.30

Question 49

What is the relative polarity of diethyl ether on SiO2?

Answer 49

0.43

Question 50

What is the relative polarity of EtOAc on SiO2?

Answer 50

0.48

Question 51

What is the relative polarity of MeCN on SiO2?

Answer 51

0.52

Question 52

What is the relative polarity of iPrOH on SiO2?

Answer 52

0.60

Question 53

What is the relative polarity of H2O on SiO2?

Answer 53

>>1

Question 54

What is the relative polarity of MeOH on SiO2?

Answer 54

0.70