SFC

Question 1

what is the properties of supercritical CO2

Answer 1

• solubility and density
• viscosity and diffusivity
  -compressibility

Question 2

how does above property effect in SFC

Answer 2

• liquid like density and solubility has effect on retention time
• solid like viscosity and diffusivity has effect on zone broadening

Question 3

explain how viscosity and density has effect in sfc

Answer 3

• density has effect on retention by considering the resolving power of the liquid.
• viscosity has effect on the efficiency

Question 4

what is the behaviour of the liquid like density at the critical point

Answer 4

at critical point, density of the gas and liquid phase are identical. the phase are indistinguishable

Question 5

what affect efficient in SFC

Answer 5

faster diffusion rate Dm due to low viscosity leading to low mass transfer resistance and higher longitudinal diffusion.
which make it better than LC

Question 6

compare SFC and HPLC considering efficiency

Answer 6

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

Question 7

pressure drop effect on SFC and LC

Answer 7

here pressure drop depends on particle size as Pressure drop is inversely proportional to the particle size

Question 8

what is the state of scCO2

Answer 8

is non-polar means has poor solubility

Question 9

what can be dissolved by scCO2

Answer 9

IT CAN DISSOLVE fats, oils and waxes

Question 10

how does density affect resolving power of co2

Answer 10

the high the density the higher resolving power of co2

Question 11

when can co2 dissolve polar compounds

Answer 11

when is mixed with co-solvent.
ex: methanol, ethanol and acetonitrile

Question 12

is it important to keep one phase of co2 and co-solvent in the column

Answer 12

yes

Question 13

how does pressure drop affect the temperature and density

Answer 13

as the pressure drop get lower the density will get reduced which cool the column and temperature get reduced too

Question 14

how does composition of co-solvent B% affect Kd and K

Answer 14

by increasing B% and density, you increase the solubility which affect Kd by increase it thus k

Question 15

how does pressure affect the retention

Answer 15

by increasing the pressure, density is increased thus the solubility which increase the elution strength which reduce retention time

Question 16

how does temperature affect retention

Answer 16

by reducing the temperature you increase the density with increase the solubility leading to increase of elution strength which reduce retention time.

Question 17

does SFC use stationary phase

Answer 17

yes, mainly used is silica

Question 18

when do we use neat scCO2 eluent

Answer 18

for very non-polar compound

Question 19

when the compound is medium polar what eluent do we use

Answer 19

we add co-solvent in the scCO2

Question 20

how does co-solvent affect the retentivity of the analyte

Answer 20

temperature change according to the mobile phase composition which is the % of the co-solvent and the type of co-solvent

Question 21

how can type of so-solvent we add in CO2 affect the elution time and temperature

Answer 21

• 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

Question 22

what does varying temperature and type of co-solvent changes

Answer 22

selectivity

Question 23

does darcy’s law affect K ans selectivity in SFC

Answer 23

yes

Question 24

how to improve resolution

Answer 24

• 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