SFC

Question 1

How do you control properties in SFC?

Answer 1

By controlling the temperature

Question 2

Give an example of what SFC can be used as

Answer 2

Removing caffeine from coffee beans

Question 3

Can supercritical CO2 dissolve oils?

Answer 3

Yes

Question 4

How do you make SFC more polar?

Answer 4

Add an organic modifier (+ additives + water if you need it very polar)

Question 5

In what way is SFC like GC and in what way is it like LC?

Answer 5

It has gas-like viscosity and diffusivity which has effect on zone spreading (like GC)
It has liquid-like density and solubility which has effect on retention (like LC)

Question 6

What does increasing the temperature mean for the density?

Answer 6

It means reducing density

Question 7

Is a supercritical fluid a two phase system?

Answer 7

Yes

Question 8

How is SFC and LC different in terms of efficiency?

Answer 8

SFC has faster diffusion rates (DM) due to lower viscosity, this lowers the mass transfer resistance (C term Van Deemter) and increases longitudinal diffusion (B term Van Deemter)

Question 9

How much more efficient is SFC than HPLC?

Answer 9

3 to 10 times

Question 10

What does supercritical CO2 dissolve?

Answer 10

oils, fats, waxes, small hydrophobic compounds

Question 11

Why does density change?

Answer 11

Because we have a pressure drop

Question 12

Are liquids incompressible?

Answer 12

Yes

Question 13

Are supercritical fluids incompressible?

Answer 13

No, supercritical fluids are compressible

Question 14

Does k and KD vary along the column due to the compressibility of the eluent?

Answer 14

Yes

Question 15

Give some examples of stationary phase SFC ligands

Answer 15

Silica
Cyano
Diol
Amide
Fluorophenyl
Octadecylsilica

Question 16

Give some examples of stationary phases of SFC columns

Answer 16

Phenyl
Pentafluorophenyl
C18
Reversed phase amide
Porous graphitic carbon

Question 17

What is the mobile phase composed of?

Answer 17

Supercritical CO2 (solubility controlled by density)
Gradients of 2 % to 40 % methanol is common

Question 18

During the supercritical fluid behaviour (at higher temp) retention increases when temperature increases and during the liquid-like behaviour (at lower temp) retention _____ when temperature increases

Answer 18

Retention decreases when temp increases during the liquid like behaviour of supercritical fluids

Question 19

Does retention depend on the co-solvent in CO2

Answer 19

Yes

Question 20

Why are mobile phase additives added?

Answer 20

To improve peak shape
To mask residual silanol groups
To enable the elution of very polar or basic compounds
Displacing the effects in case of ion exchange mechanism

Question 21

What are some common additives?

Answer 21

For polar organic acids: formic acid, TFA, citric acid
Basic: isopropyl amine, TEA
Water can be used as additive

Question 22

Does the pressure affect SFC?

Answer 22

Yes

Question 23

Does the temperature affect SFC?

Answer 23

Yes

Question 24

Does the density affect SFC?

Answer 24

Yes

Question 25

Is SFC much better than LC from a green viewpoint?

Answer 25

Yes

Question 26

Is SFC normal phase?

Answer 26

Yes

Question 27

What parameters affect selectivity?

Answer 27

Type of stationary phase
Type of eluent components
Temperature

Question 28

What does selectivity depend on?

Answer 28

Analyte properties, intermolecular interactions with phases

Question 29

What does chromatographic efficiency depend on?

Answer 29

Longitudinal diffusion (B)
Resistance to mass transfer (C)

Question 30

What does retentivity depend on?

Answer 30

Intermolecular interactions
Solvating power (elution strength of MP)

Question 31

Do flow rates affect the pressure?

Answer 31

Yes