SFC Flashcards
How do you control properties in SFC?
By controlling the temperature
Give an example of what SFC can be used as
Removing caffeine from coffee beans
Can supercritical CO2 dissolve oils?
Yes
How do you make SFC more polar?
Add an organic modifier (+ additives + water if you need it very polar)
In what way is SFC like GC and in what way is it like LC?
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)
What does increasing the temperature mean for the density?
It means reducing density
Is a supercritical fluid a two phase system?
Yes
How is SFC and LC different in terms of efficiency?
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)
How much more efficient is SFC than HPLC?
3 to 10 times
What does supercritical CO2 dissolve?
oils, fats, waxes, small hydrophobic compounds
Why does density change?
Because we have a pressure drop
Are liquids incompressible?
Yes
Are supercritical fluids incompressible?
No, supercritical fluids are compressible
Does k and KD vary along the column due to the compressibility of the eluent?
Yes
Give some examples of stationary phase SFC ligands
Silica
Cyano
Diol
Amide
Fluorophenyl
Octadecylsilica
Give some examples of stationary phases of SFC columns
Phenyl
Pentafluorophenyl
C18
Reversed phase amide
Porous graphitic carbon
What is the mobile phase composed of?
Supercritical CO2 (solubility controlled by density)
Gradients of 2 % to 40 % methanol is common
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
Retention decreases when temp increases during the liquid like behaviour of supercritical fluids
Does retention depend on the co-solvent in CO2
Yes
Why are mobile phase additives added?
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
What are some common additives?
For polar organic acids: formic acid, TFA, citric acid
Basic: isopropyl amine, TEA
Water can be used as additive
Does the pressure affect SFC?
Yes
Does the temperature affect SFC?
Yes
Does the density affect SFC?
Yes
Is SFC much better than LC from a green viewpoint?
Yes
Is SFC normal phase?
Yes
What parameters affect selectivity?
Type of stationary phase
Type of eluent components
Temperature
What does selectivity depend on?
Analyte properties, intermolecular interactions with phases
What does chromatographic efficiency depend on?
Longitudinal diffusion (B)
Resistance to mass transfer (C)
What does retentivity depend on?
Intermolecular interactions
Solvating power (elution strength of MP)
Do flow rates affect the pressure?
Yes
