Question

Noye-Whitney’s equation predicts:

• A. An increase of dissolution rate if the particle size is reduced by micronization because of an increase in area
• B. relationship between the radius of the diffusing molecule and its diffusion coefficient
• C. The influence of electrolyte on the rate rate constant
• D. An equilibrium between the surfactant and the drug molecules at the surface of the solution and in the bulk of the solution.

Answer 1

The Correct Option is A

The question is related to the Noyes-Whitney equation, which is fundamental in pharmaceutics for understanding the dissolution process of drugs. Let's go through the options to identify the correct answer:

1. An increase of dissolution rate if the particle size is reduced by micronization because of an increase in area: This directly relates to the Noyes-Whitney equation, which expresses the dissolution rate (\( \frac{dC}{dt} \)) as: \frac{dC}{dt} = \frac{DA(C_s - C)}{L} Here, \( D \) is the diffusion coefficient, \( A \) is the surface area of the particle, \( C_s \) is the saturation concentration, \( C \) is the concentration at time \( t \), and \( L \) is the thickness of the diffusion layer. According to the equation, the dissolution rate increases when the surface area \( A \) increases. This happens when particle size is reduced, as smaller particles increase the total surface area available for dissolution.
2. Relationship between the radius of the diffusing molecule and its diffusion coefficient: While this is true in the context of diffusion, it pertains more to the Stokes-Einstein equation rather than the Noyes-Whitney equation.
3. The influence of electrolyte on the rate constant: This is not directly addressed by the Noyes-Whitney equation, which focuses on dissolution rates and does not specifically account for the effect of electrolytes on the rate constant.
4. An equilibrium between the surfactant and the drug molecules at the surface of the solution and in the bulk of the solution: This is more related to surfactant chemistry and adsorption phenomena, rather than the dissolution rate and is not covered by the Noyes-Whitney equation.

Therefore, the correct answer is: An increase of dissolution rate if the particle size is reduced by micronization because of an increase in area.