Lecture 6 - Intro into Dissolution and Solubility Flashcards
Solubility of a substance
amount that goes into solution when equilibrium is established between the solute in solution and the excess (undissolved) substance
Solution
mixture of 2 or more components that form a single, homogeneous phase
Dissolution
PROCESS by which a solid dissolves in a solvent to produce a solution
Why do drug solutions work quicker than capsules/tablets?
Because in order to be absorbed, drug must be in liquid form, therefore if already a liquid it will act quicker
What does increased surface area do to dissolution rate?
increases it as solvent can come in contact more with the solute therefore dissolving it quicker. Porous drugs also speed this up.
Process of dissolution
molecule leaves solid, diffuses across h (determines the rate), molecule leaves diffuse layer for well-stirred bulk
Noyes-Whitney Equation use?
allows you to work out dissolution rate of drug particles
Diffusion Layer
drug surrounded in solvent
Noyes-Whitney Equation
dm/dt = da x Cs-C/h
what is D in NWE
diffusion coefficient
What is A in NWE
effective surface area of drug particles
what is H in NWE
thickness of diffusion layer
What is Cs in NWE?
Saturated solubility
C in NWE
Concentration in the bulk solubility
Factors affecting dissolution rates
- Increasing surface area increases dissolution rate, therefore small particles high dissolution rate
- Porous particles are openings solvents can enter in, also increasing dissolution rate.
- Using appropriate solvent and at optimum temp.
- Dissolution slower in viscous solvents, dissolution coefficient is mostly dependant on viscosity of solvent
Agitation (stirring) decreases diffusion layer therefore increasing dissolution rate
