SFC Flashcards
what is the properties of supercritical CO2
- solubility and density
- viscosity and diffusivity
-compressibility
how does above property effect in SFC
- liquid like density and solubility has effect on retention time
- solid like viscosity and diffusivity has effect on zone broadening
explain how viscosity and density has effect in sfc
- density has effect on retention by considering the resolving power of the liquid.
- viscosity has effect on the efficiency
what is the behaviour of the liquid like density at the critical point
at critical point, density of the gas and liquid phase are identical. the phase are indistinguishable
what affect efficient in SFC
faster diffusion rate Dm due to low viscosity leading to low mass transfer resistance and higher longitudinal diffusion.
which make it better than LC
compare SFC and HPLC considering efficiency
SFC gas-like diffusivity and low viscosity make us achieve minimum at high flow rate.
. due to low viscosity, pressure drop will be lower too as they are directly proportional. so we will have lower pressure drop over the column.
. so by using longer column with high flow rate, this will increase plate number causing better efficiency.
. SFC is 3 times more sufficient than HPLC
pressure drop effect on SFC and LC
here pressure drop depends on particle size as Pressure drop is inversely proportional to the particle size
what is the state of scCO2
is non-polar means has poor solubility
what can be dissolved by scCO2
IT CAN DISSOLVE fats, oils and waxes
how does density affect resolving power of co2
the high the density the higher resolving power of co2
when can co2 dissolve polar compounds
when is mixed with co-solvent.
ex: methanol, ethanol and acetonitrile
is it important to keep one phase of co2 and co-solvent in the column
yes
how does pressure drop affect the temperature and density
as the pressure drop get lower the density will get reduced which cool the column and temperature get reduced too
how does composition of co-solvent B% affect Kd and K
by increasing B% and density, you increase the solubility which affect Kd by increase it thus k
how does pressure affect the retention
by increasing the pressure, density is increased thus the solubility which increase the elution strength which reduce retention time
how does temperature affect retention
by reducing the temperature you increase the density with increase the solubility leading to increase of elution strength which reduce retention time.
does SFC use stationary phase
yes, mainly used is silica
when do we use neat scCO2 eluent
for very non-polar compound
when the compound is medium polar what eluent do we use
we add co-solvent in the scCO2
how does co-solvent affect the retentivity of the analyte
temperature change according to the mobile phase composition which is the % of the co-solvent and the type of co-solvent
how can type of so-solvent we add in CO2 affect the elution time and temperature
- by adding methanol and acetonitrile. due to their supercritical fluid- special behaviour, temperature increase with increase of retention.
- by adding ethanol. due to its liquid like behaviour, temperature increase with decrease of the retention
what does varying temperature and type of co-solvent changes
selectivity
does darcy’s law affect K ans selectivity in SFC
yes
how to improve resolution
- Retentivity: you can increase retention time by reducing elution strength of mobile phase and changing B% composition in CO2.
- Efficiency: can be increased with
longitudinal diffusion by changing
Diffusivity and mass transfer resistance by changing Viscosity - selectivity: which is affected by temperature and stationary phase and type of eluent component
