22 Questions
What happens to particles in an electrophoresis cell when a potential is applied?
They migrate to the oppositely charged electrode.
How is the zeta potential of colloidal dispersions determined?
Through electrophoretic light scattering.
What is the purpose of freeze-thaw cycling?
To prepare a suspension for measurement.
What is measured to determine the rate of migration of particles?
The velocity of particle migration.
What is proportional to the velocity of particle migration?
Zeta potential.
What is used to determine the particle speed in electrophoretic light scattering?
Specialized formulas.
What is the outcome of crystal bridging in a particulate system?
Creation of a highly linked sediment similar to concrete
What is a contributing factor to the formation of crystal bridges?
Temperature fluctuation
What is the process by which larger particles grow at the expense of smaller ones?
Ostwald ripening
Why do smaller particles have a higher dissolution rate per unit mass?
Due to their larger surface area
What is the result of Ostwald ripening on the particle size spectrum?
A shift to larger particle sizes
What accelerates crystal growth and Ostwald ripening?
Temperature fluctuations
What is the consequence of Ostwald ripening on the suspension?
The suspension becomes coarser
What is the driving force behind Ostwald ripening?
Concentration gradient
What is the primary factor that determines the effects of temperature fluctuations on a drug's solubility and re-crystallization?
The magnitude of temperature change
What is the allowed temperature range for controlled room temperature, according to USP General Chapter?
15°-30° (59°-86 °F)
What is the maximum allowed temperature spike in controlled room temperature, according to USP General Chapter?
40° (104 °F)
What is the potential consequence of Ostwald ripening and crystal growth in a solid dispersion?
All of the above
What is one strategy to prevent crystal growth and changes in particle size distributions in a solid dispersion?
Using a dispersion medium with lowest drug solubility
What is the purpose of incorporating wetting agents and protective colloids in a solid dispersion?
To inhibit crystal growth
What is the potential benefit of selecting a more stable crystalline form of the drug in a solid dispersion?
Reduced risk of crystal growth
Why is it important to avoid high energy milling during particle size reduction in a solid dispersion?
To prevent crystal growth
Study Notes
Solid Bridging and Related Phenomena
- Crystal bridging leads to the formation of crystal-linked particles, resulting in a highly linked sediment similar to concrete.
- Contributors to crystal bridging include saturated solutions, temperature fluctuations, and particle surface crystal growth on multiple particles simultaneously.
Ostwald Ripening
- Ostwald ripening is the growth of larger particles at the expense of smaller ones due to differences in dissolution rates.
- Smaller particles have a greater surface area and higher dissolution rates, leading to a concentration gradient and diffusion of drug molecules towards larger particles.
- This results in crystallization, particle growth, and a coarser suspension with a mean particle size spectrum shifted to higher values.
Temperature Fluctuations
- Temperature fluctuations during storage accelerate crystal growth and Ostwald ripening.
Electrophoresis and Zeta Potential
- Electrophoresis measures the migration rate of particles in an electric field, allowing calculation of zeta potential, which is proportional to particle velocity.
- Zeta potential can also be measured using electrophoretic light scattering, which detects the frequency shift of a laser beam scattered by particles.
Particle Size Analysis and Sedimentation
- Particle size analysis is typically performed after preparing a suspension and subjecting it to freeze-thaw cycling.
- Sedimentation methods involve measuring sedimentation ratios and flocculation ratios (β).
Temperature Control and Storage
- Controlled room temperature is defined as 20-25°C (68-77°F), with allowable excursions between 15-30°C (59-86°F) and transient spikes up to 40°C for short periods.
- The mean kinetic temperature should not exceed 25°C.
Crystal Growth and Ostwald Ripening Prevention
- To prevent problems associated with crystal growth and changes in particle size distributions, strategies include:
- Using a dispersion medium with low drug solubility
- Selecting particles with a narrow size range
- Choosing a more stable crystalline form of the drug
- Avoiding high-energy milling during particle size reduction
- Incorporating wetting agents and protective colloids to inhibit crystal growth.
Learn about crystal bridging, a process where particle surface crystal growth occurs on two or more particles, leading to the formation of a highly linked sediment. Discover the contributors to this phenomenon.
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