Sedimentation and Particle Size Quiz

Questions and Answers

What happens to particles if the size is decreased too much in a suspension?

They enhance the re-dispersibility of the product.

They increase the velocity of sedimentation.

They dissolve completely in the dispersion medium.

They can form a compact cake upon settling. (correct)

How is the velocity of sedimentation related to the viscosity of the dispersion medium?

Proportional only when particle size is increased.

Independent, as particle size does not affect sedimentation velocity.

Inversely proportional, meaning higher viscosity decreases sedimentation velocity. (correct)

Directly proportional, meaning higher viscosity increases sedimentation velocity.

What is a disadvantage of using a product with very high viscosity in suspensions?

It increases the sedimentation velocity.

It makes the removal of the product from the container difficult. (correct)

It changes the pH of the suspension.

It enhances the sweetness of the suspension.

What is the maximum concentration of a particulate substance in a dilute pharmaceutical suspension?

Less than 2gm per 100 ml. Signup and view all the answers

Which type of suspension must contain suitable flavoring and sweetening agents?

Oral suspensions. Signup and view all the answers

What should topical suspensions be free from to ensure patient comfort?

Gritty particles. Signup and view all the answers

What property must parenteral suspensions possess?

They must be sterile and possess syringability. Signup and view all the answers

What characteristics should ophthalmic suspensions have?

They must be sterile and composed of very fine particles. Signup and view all the answers

What characterizes deflocculated suspensions in terms of particle behavior?

Particles exist as separate entities in the dispersion medium. Signup and view all the answers

Which factors influence the rate of sedimentation in a suspension?

Temperature of the liquid and viscosity of the medium. Signup and view all the answers

What is a key feature of flocculated suspensions compared to deflocculated suspensions?

Flocculated suspensions are more turbid over time. Signup and view all the answers

What is the effect of particle size distribution on sedimentation?

Larger particles settle more rapidly than smaller ones. Signup and view all the answers

Which type of solid particles are more prone to forming a hard cake when settling?

Deflocculated solid particles. Signup and view all the answers

What describes the turbidity of the supernatant in flocculated suspensions?

It is always turbid for an extended period. Signup and view all the answers

Which preparation method primarily involves precipitate forming liquids?

Precipitation from metered solutions. Signup and view all the answers

Which type of suspension maintains a more elegant uniform appearance over time?

Flocculated suspension. Signup and view all the answers

What is the advantage of using a structured vehicle in suspensions?

It increases the viscosity and helps maintain flocculated particles. Signup and view all the answers

How does particle size control contribute to suspension stability?

It helps avoid changes in particle size distribution. Signup and view all the answers

What is a disadvantage of using structured vehicles in suspensions?

They can lead to caking of sediment. Signup and view all the answers

What property of structured vehicles facilitates uniform dispersion upon application of shear?

Thixotropic behavior. Signup and view all the answers

What is the effect of small particle size in suspensions?

It controls the rate of dissolution of the drug. Signup and view all the answers

Which statement describes flocculation in the context of suspensions?

Flocculation leads to larger, more easily resuspendable aggregates. Signup and view all the answers

Which type of flow is desirable for structured vehicles used in suspensions?

Pseudoplastic flow. Signup and view all the answers

What aspect of particle size can compromise the stability of a suspension?

Changes in particle size distribution. Signup and view all the answers

Study Notes

Particle Size and Sedimentation

Fine particles can create a compact cake upon settling, complicating re-dispersibility.
Sedimentation velocity equation:
- ( V = \frac{d^2 g (\sigma - \rho)}{18 \eta} ), where:
  - ( V ) = sedimentation velocity (cm/sec)
  - ( d ) = particle diameter (cm)
  - ( \sigma ) = density of solid particles
  - ( \rho ) = density of dispersion phase
  - ( g ) = acceleration due to gravity
  - ( \eta ) = viscosity of the dispersion phase (poise).
High viscosity in products complicates removal and re-dispersibility.

Classification of Suspensions

Oral suspensions require flavoring and sweetening agents.
Topical suspensions must be free from gritty particles for external application.
Parenteral suspensions should be sterile and easily syringable.
Ophthalmic suspensions need to be sterile and consist of fine particles.

Sedimentation Characteristics

Slow sedimentation leads to loose aggregates that can be easily re-dispersed.
Fast sedimentation can cause caking, making re-dispersion difficult.
The final volume of sediment can vary significantly depending on particle properties.

Developing Stable Suspensions

Utilizing structured vehicles increases viscosity to keep flocculated particles in suspension, ideally preventing settling.
Control of particle size is crucial for suspension stability.
Wetting agents can enhance dispersibility.
Flocculation principles can create easily resuspendable flocs that settle rapidly.

Structured Vehicles

Structured vehicles should ideally exhibit pseudoplastic and plastic properties, enabling thixotropic behavior.
They entrap deflocculated particles to prevent settling while facilitating uniform dispersion upon shear application.
Aim for optimal stability using flocculated particles in a hydrophilic colloid.

Particle Size Advantages

Maintaining small particle size controls dissolution rates and consistency in formulation.
Considerations for dispersed phase include diffusible, in-diffusible, and poorly wettable solids.
Preparation methods can involve precipitate-forming liquids and products of chemical reactions.

Nature of Sediment

Flocculated Suspensions:
- Solid particles aggregate forming a network, settling slowly due to lower sedimentation rates.
- Easily re-dispersible; not elegant in appearance.
Deflocculated Suspensions:
- Solid particles remain as individual entities creating a hard sediment cake.
- Settle rapidly with a clear boundary between sediment and supernatant.

Types of Suspensions

Controlled flocculation is necessary to optimize sedimentation rate, sediment characteristics, and pourability.
Deflocculated suspensions show turbid supernatant and rapid sedimentation while flocculated suspensions maintain clarity for longer periods, appearing more elegant.

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Description

This quiz explores the principles of sedimentation and the effects of particle size on sedimentation velocity. Understand the balance needed to prevent fine particles from forming compact cakes upon settling. Test your knowledge with questions focused on these critical concepts.