Dissolution Of Solids Flashcards
3 steps of dissolution mechanisms
1) solute molecule leaves particle
2) creation of a cavity in the solvent
3) solute molecule enters the cavity
What is the symbol for boundary layer?
h ( italic)
What is the symbol for a saturated boundary layer?
Cs
What is the symbol for the bulk?
C
How does the solute diffuse through the layers?
Boundary layer becomes saturated almost instantaneously. Solute diffusion from the boundary layer into the bulk solvent takes more time.
What is the Noyes-Whitney equation used for?
This process of mass transfer change with time effectively determines the rate of dissolution for pharmaceutical solids.
What is the symbol for mass transfer change in the Noyes-Whitney equation?
dm
What is the symbol for time in the Noyes-Whitney equation?
dt
What is the Noyes-Whitney equation?
dm =k1 A (CS-C)
—- —————
dt. h
What does k1 stand for in the Noyes-Whitney equation?
Dissolution of rate constant
What does A stand for in the Noyes-Whitney equation?
Surface area of undissolved solid drug
What does CS stand for in the Noyes-Whitney equation?
Saturated solubility of drug in solid in solvent.
What does C stand for in the Noyes-Whitney equation?
Concentration of drug in solution at time
What does h stand for in the Noyes-Whitney equation?
Thickness of boundary layer
how can we speed up the dissolution process?
increase surface area/ reduce particle size
increasing the temperature
changing the solvent/ adding a cosolvent
increase the volume of the solvent
remove dissolved drug from the solution
agitation of the drug in the dissolution medium
