colloid & suspension(medium+hard)
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Questions and Answers

What is the outcome of particles in a deflocculated suspension?

  • Formation of loose aggregates that sediment slowly
  • Large sediment volume with bulky flocs
  • Rapid sedimentation and easy redispersion
  • Cloudy supernatant with individual particles present (correct)

Why are pharmaceutical suspensions preferred over solid dosage forms?

  • They are less effective in taste masking.
  • They provide higher stability against hydrolysis. (correct)
  • They are easier to aggregate and store.
  • They have lower surface area than solid forms.

What characteristic does a fully flocculated system exhibit?

  • Cloudy supernatant with dense particles
  • Difficult to redisperse due to packed particles
  • Large sediment volume with rapid sedimentation (correct)
  • Minimal sediment volume with easy redispersion

What is the main problem associated with deflocculated suspensions?

<p>They can form a cake during settling. (C)</p> Signup and view all the answers

Which of the following describes a key feature of a flocculated suspension?

<p>Loose clusters that easily redispersed on shaking (A)</p> Signup and view all the answers

What is the effect of Stokes' law on particle behavior in a flocculated suspension?

<p>It leads to rapid reforming and sedimentation of flocs. (A)</p> Signup and view all the answers

When classifying suspensions, which factor is NOT considered?

<p>Rate of particle growth (D)</p> Signup and view all the answers

Which of the following statements describes the characteristics of a deflocculated suspension?

<p>It retains strong van der Waals forces leading to cake formation. (D)</p> Signup and view all the answers

What is the significance of particle surface area in the formulation of suspensions?

<p>High surface area helps in achieving better taste masking. (A)</p> Signup and view all the answers

What is a defining characteristic of colloidal particles?

<p>They have at least one dimension between 1 nm to 1 µm. (B)</p> Signup and view all the answers

Which of the following is an example of a lyophobic colloid?

<p>Oily phases (D)</p> Signup and view all the answers

Why are lyophobic dispersions considered thermodynamically unstable?

<p>They have a high surface area that can lead to coalescence. (B)</p> Signup and view all the answers

What is meant by 'disperse phase' in a colloidal system?

<p>The phase that is subdivided and dispersed within another phase. (B)</p> Signup and view all the answers

What distinguishes lyophilic colloids from lyophobic colloids?

<p>Lyophilic colloids are water-soluble; lyophobic are not. (C)</p> Signup and view all the answers

Which of the following is true about the size of colloidal particles?

<p>They fall into a size range of 10$^{-9}$ m to 10$^{-6}$ m. (A)</p> Signup and view all the answers

What does a colloidal system primarily use for drug delivery?

<p>Colloidal systems (A)</p> Signup and view all the answers

Which of the following systems can be classified as colloids?

<p>Paints and cosmetics (A)</p> Signup and view all the answers

What defines a colloidal solution when water is the solvent?

<p>Formed spontaneously and thermodynamically stable (B)</p> Signup and view all the answers

Which of the following is an example of a liquid/liquid emulsion?

<p>Milk (B)</p> Signup and view all the answers

What is the primary kinetic property that prevents the destruction of colloidal systems?

<p>Brownian motion (C)</p> Signup and view all the answers

According to Stokes' law, what factors affect the velocity of sedimentation for spherical particles?

<p>Diameter, density difference, and dynamic viscosity (C)</p> Signup and view all the answers

What is the formula used to calculate the velocity of sedimentation?

<p>V = (2 * r^2 * g * (σ - ρ)) / (9 * η) (B)</p> Signup and view all the answers

Which option would likely increase the velocity of sedimentation for a particle?

<p>Increasing the size of the particles (D)</p> Signup and view all the answers

What happens to a colloidal system when aggregation occurs?

<p>The particles become larger and may lead to instability. (D)</p> Signup and view all the answers

How does Brownian motion influence colloidal systems?

<p>It enhances the stability of the colloidal system. (A)</p> Signup and view all the answers

What is the primary advantage of using a narrow particle size range for suspended drugs?

<p>It controls the rate of drug release and bioavailability. (B)</p> Signup and view all the answers

Which thickening agent is NOT mentioned as a modifier for viscosity?

<p>Xanthan gum (A)</p> Signup and view all the answers

What characteristic of large particles, greater than 5 μm diameter, is NOT a concern during formulation?

<p>Enhancing drug absorption. (B)</p> Signup and view all the answers

What is the formula for calculating the sedimentation volume ratio?

<p>F = V/Vo (A)</p> Signup and view all the answers

Which factor does NOT contribute to the issues related to flocculated systems?

<p>Difficulty in redispersal. (A)</p> Signup and view all the answers

Which of the following is an example of a potential irritation caused by large particles in formulations?

<p>Irritation if injected or instilled into the eyes. (C)</p> Signup and view all the answers

Which thickening agent is commonly used to control viscosity in suspensions?

<p>Acacia (C)</p> Signup and view all the answers

What risk is associated with using particles greater than 25 μm in diameter?

<p>They may block hypodermic needles. (D)</p> Signup and view all the answers

What is the primary reason for using a flocculated system in pharmaceutical suspensions?

<p>It allows for rapid redispersion of particles. (C)</p> Signup and view all the answers

Which of the following best describes the sedimentation behavior of fully deflocculated suspensions?

<p>Cloudy supernatant with small sediment volume. (D)</p> Signup and view all the answers

Why is sedimentation considered a significant problem in pharmaceutical suspensions?

<p>It hinders the delivery of a uniform dose. (B)</p> Signup and view all the answers

What type of particle interaction characterizes a deflocculated system?

<p>Strong van der Waals forces leading to cake formation. (B)</p> Signup and view all the answers

How does Fick's first law relate to the diffusion of colloidal particles?

<p>It shows that particles diffuse from areas of high to low concentration. (D)</p> Signup and view all the answers

In the formulation of a pharmaceutical suspension, what is an ideal characteristic of the mixed system?

<p>Partial flocculation allowing gradual sedimentation. (C)</p> Signup and view all the answers

What factor does NOT contribute to the classification of types of suspensions?

<p>Size of the dispersed particles. (B)</p> Signup and view all the answers

What is the consequence of cake formation in a deflocculated suspension?

<p>Complicates the process of redistributing the drug. (A)</p> Signup and view all the answers

Which of the following is NOT a major problem associated with pharmaceutical suspensions?

<p>Foaming (D)</p> Signup and view all the answers

Which statement accurately describes the behavior of particles in the ideal suspension?

<p>They sediment slowly allowing for uniform dosing. (C)</p> Signup and view all the answers

What is the primary mechanism by which particles in colloidal systems maintain stability?

<p>Brownian motion and random collisions (C)</p> Signup and view all the answers

Which of the following factors is NOT associated with increasing the velocity of sedimentation in a colloidal system?

<p>Increasing the dispersing medium density (D)</p> Signup and view all the answers

In a colloidal system, what is the significance of Stokes' law?

<p>It quantifies the sedimentation velocity of particles. (A)</p> Signup and view all the answers

How does the density difference between a particle and its dispersion medium affect sedimentation?

<p>Larger density differences increase sedimentation velocity. (A)</p> Signup and view all the answers

What effect does Brownian motion have on fine particles suspended in a fluid?

<p>It maintains the suspension of particles by causing random motion. (B)</p> Signup and view all the answers

When applying Stokes' law, what would result in a reduction of sedimentation velocity in colloidal systems?

<p>Decreasing the density difference between phases (A)</p> Signup and view all the answers

In the context of colloids, what does the term 'thermodynamically stable' imply about hydrophilic systems?

<p>They can spontaneously form without external energy. (B)</p> Signup and view all the answers

What is the effect of reducing particle size in a colloidal dispersion?

<p>It enhances system stability and decreases sedimentation velocity. (D)</p> Signup and view all the answers

What is a defining characteristic of lyophobic colloids?

<p>They are thermodynamically unstable and may separate. (A)</p> Signup and view all the answers

Which size range is typical for colloidal particles?

<p>From 1 nm to 1 μm (B)</p> Signup and view all the answers

Why are lyophobic colloids problematic in formulation?

<p>They require extensive processing to remain stable. (D)</p> Signup and view all the answers

What is a common use of colloidal systems in pharmaceuticals?

<p>Controlling the release of drug compounds (A)</p> Signup and view all the answers

What is one challenge faced when distinguishing between colloidal and non-colloidal particles?

<p>Size ranges can often overlap with larger particles. (D)</p> Signup and view all the answers

Which of the following statements about colloidal particles is true?

<p>They lie between true solutions and coarse suspensions. (B)</p> Signup and view all the answers

What is the primary function of thickening agents in suspensions?

<p>To modify the viscosity of the vehicle (B)</p> Signup and view all the answers

Which of the following is a primary concern when formulating a suspension with particles larger than 5 μm in diameter?

<p>Possibility of blocking hypodermic needles (A)</p> Signup and view all the answers

What does a higher particle size distribution (polydispersity) in a drug suspension lead to?

<p>Formation of very small crystals (B)</p> Signup and view all the answers

What is the relationship between viscosity and sedimentation rate in a suspension?

<p>Increased viscosity tends to minimize sedimentation rate (C)</p> Signup and view all the answers

Which statement accurately describes the sedimentation volume ratio (F) in a suspension formulation?

<p>F equals the ratio of final sediment volume to the original total volume (C)</p> Signup and view all the answers

Which of the following thickening agents is NOT commonly used to modify viscosity in suspensions?

<p>Maltodextrin (A)</p> Signup and view all the answers

What is the potential issue with using large particles in a formulation that exceed 25 μm in diameter?

<p>They can cause irritation when injected (D)</p> Signup and view all the answers

Which characteristic is NOT associated with flocculated suspensions?

<p>Increased elegance of formulation (B)</p> Signup and view all the answers

Flashcards

What are colloidal particles?

Colloidal particles are small particles dispersed in a medium, larger than molecules but smaller than coarse suspensions. They are visible with an electron microscope and cannot pass through semi-permeable membranes.

What are lyophobic colloids?

Lyophobic colloids are 'solvent hating'; they include substances like water-insoluble drugs, clays, oil phases, suspensions of microorganisms, blood, and metals.

What are lyophilic colloids?

Lyophilic colloids are 'solvent loving'; these include substances like surfactants, proteins, and gums. They naturally dissolve in the solvent.

Why are lyophobic colloids unstable?

Lyophobic colloids are thermodynamically unstable and tend to separate over time. This is due to their high surface area, which favors a decrease in surface area through aggregation or coalescence.

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What is the difference between the disperse phase and the continuous phase?

The 'disperse phase' is the phase that is divided into tiny particles, while the 'continuous phase' is the medium in which the particles are dispersed. For example, in milk, the fat droplets are the disperse phase, and the water is the continuous phase.

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What is the size range for colloidal particles?

The size of colloidal particles falls between 1 nanometer (nm) and 1 micrometer (µm). This means they are much larger than molecules but much smaller than coarse suspensions.

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How are colloidal systems used in medicine?

Colloidal systems are used for drug delivery and nanoparticle technology. By controlling the size and properties of the colloidal particles, we can achieve targeted drug delivery and improve the effectiveness of medications.

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Where are colloidal systems found?

Colloidal systems are found in many everyday products, including aerosols, cosmetics, paint, cement, rubber, and pharmaceuticals. These systems often have unique properties that are beneficial for different applications.

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What are colloids?

Colloids are mixtures where one substance is dispersed evenly throughout another, forming a stable system.

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What are hydrophilic colloids?

Hydrophilic colloids are colloids where the dispersed phase (the particles) readily interact with water, the solvent.

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What is Brownian motion?

The random movement of colloidal particles caused by collisions with molecules of the dispersing medium.

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How does Brownian motion affect colloids?

Brownian motion is the random movement of colloidal particles caused by collisions with molecules of the dispersing medium.

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What is Stokes' Law?

Stokes' Law describes the rate of sedimentation or creaming of spherical particles in a liquid. The velocity depends on the particle's size, density, and the liquid's viscosity.

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What is sedimentation?

The separation of particles in a colloid, where denser particles settle to the bottom.

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What is creaming?

The separation of particles in a colloid, where less dense particles rise to the top.

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How can we slow down sedimentation or creaming?

Smaller particle size, higher viscosity of the liquid, and a smaller density difference between the particles and the liquid all reduce the rate of sedimentation or creaming.

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Flocculated suspension

A suspension that forms loose, easily redispersed sediments, but settles quickly, risking inaccurate dosage and an unappealing appearance.

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Size reduction in suspensions

The process of reducing the size of solid particles in a suspension.

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Why is particle size important in suspensions?

Particles larger than 5 μm in a suspension can cause gritty texture, irritation, or blockage.

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Particle size range

The range of particle sizes in a suspension.

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Importance of particle size range for drug release

Using a specific particle size range helps control drug release rate and bioavailability.

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Monodispersed suspension

A suspension where all particles are roughly the same size.

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Polydispersed suspension

A suspension with a wide range of particle sizes.

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Thickening agents in suspensions

Substances that increase the viscosity of a suspension, improving stability and preventing settling.

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Diffusion in Colloids

Colloidal particles move from areas of high concentration to low concentration, like a crowd spilling out of a crowded room.

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What is a pharmaceutical suspension?

A suspension is a mixture of insoluble drug particles dispersed in a liquid. It can be colloidal (very small particles) or coarser (larger particles that settle more easily).

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Why use suspensions?

Suspensions are used when a drug is difficult to swallow in solid form, needs to be stable over time, or has a bad taste. They also allow for a high surface area of the drug for better absorption.

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Common problems with suspensions

Sedimentation is the settling of particles to the bottom due to gravity. Caking is when particles clump together forming a hard mass. Flocculation is the formation of loose clumps of particles. Particle growth is when particles dissolve and re-crystallize leading to larger particles.

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How are suspensions classified?

Suspensions can be classified based on the liquid used (water or oil), how the particles are arranged (flocculated or deflocculated), and the drug's stability (stable or needs reconstitution).

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What is flocculation?

Flocculation is the formation of loose clusters of particles in a suspension. This helps to prevent caking and makes the suspension easier to redisperse.

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Characteristics of a flocculated suspension

A flocculated suspension has a clear supernatant (liquid on top), large sediment volume (lots of loose clumps), rapid sedimentation (particles settle quickly), and is easily redispersed by shaking.

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Characteristics of a deflocculated suspension

A deflocculated suspension has a cloudy supernatant (liquid on top), small sediment volume (particles tightly packed), slow sedimentation (particles settle slowly), and is difficult to redisperse.

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What is partial flocculation?

Partial flocculation involves creating a balance between deflocculated and flocculated states. This leads to slower sedimentation and easier redispersion, while still maintaining a reasonably stable suspension.

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Why are deflocculated systems not ideal for pharmaceuticals?

Deflocculated systems can face problems like slow sedimentation and caking due to tightly packed particles. It's generally less desirable for pharmaceutical suspensions.

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What is the disperse phase?

The phase that is subdivided and dispersed in the continuous phase. For example, in milk, the fat droplets are the disperse phase, and the water is the continuous phase.

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What is the continuous phase?

The phase that surrounds and holds the dispersed phase. For example, in milk, the water is the continuous phase, and the fat droplets are the disperse phase.

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Are colloids stable?

Colloids formed spontaneously and are thermodynamically stable. If water is the solvent, they are called hydrophilic.

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Define sedimentation and creaming.

Sedimentation refers to denser particles settling to the bottom, while creaming involves less dense particles rising to the top in a colloid.

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How to slow down sedimentation or creaming?

To slow down sedimentation or creaming, form smaller particles, increase liquid viscosity, or reduce the density difference between the phases.

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Size Reduction

The process of reducing the size of solid particles in a suspension, typically by grinding or milling.

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Particle Size Limit in Suspensions

Particles larger than this size may give a gritty texture to a suspension, cause irritation, or block needles during injection.

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Thickening Agents

Used to increase the viscosity of a suspension, preventing rapid sedimentation and improving stability.

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Sedimentation Volume Ratio (F)

The measure of a suspension's stability, calculated by dividing the volume of settled sediment by the total volume of the suspension.

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Pharmaceutical Suspension

A mixture of an insoluble drug dispersed in a liquid, either colloidal (small particles) or coarser (larger particles that settle more easily).

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Sedimentation

The settling of particles to the bottom of a suspension due to gravity. This can lead to uneven dosing and an unattractive appearance.

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Caking

The process of particles clumping together to form a hard, solid mass at the bottom of a suspension. This makes it difficult to redisperse the suspension.

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Flocculation

The formation of loose clumps of particles in a suspension. This is a controlled process used to prevent caking and maintain a stable suspension.

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Particle Growth

The process of drug particles dissolving and then re-crystallizing, leading to larger particles in a suspension. This can affect drug stability and bioavailability.

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Study Notes

MPharm Programme - Colloids & Suspensions

  • Colloids are large molecules or finely divided particles dispersed in a medium. They lie between true solutions and coarse suspensions.
  • Colloidal particles are visible with an electron microscope but not through semi-permeable membranes.
  • Their size ranges from 10⁻⁹ m to 10⁻⁶ m, with at least one dimension between 1 nm and 1 μm.
  • All three dimensions are not always in the colloidal range (e.g., fibers).
  • Distinguishing colloidal from non-colloidal systems can be challenging.
  • Examples of colloidal systems include aerosols, cosmetics, paints, cement, rubber, and pharmaceuticals. These applications often use colloidal systems for drug delivery and nanotechnology applications.

Classification of Colloidal Particles

  • Lyophobic colloids are solvent-hating (e.g., water-insoluble drugs, clays, oily phases, suspensions of microorganisms, blood, and metals).

  • Lyophobic dispersions are not spontaneously formed in the medium.

  • They are thermodynamically unstable and will separate (although some may remain suspended for extended periods).

  • Size and high surface area contribute to the instability by affecting free energy (reducing surface area is favorable).

  • Be aware that some water-insoluble drugs, like kaolin, are often classified as lyophobic but not 'water-hating'

  • Lyophilic colloids are solvent-loving (e.g., surfactants, proteins, gums).

  • These solutions (colloidal, not true) form spontaneously, making them thermodynamically stable.

  • These are termed 'hydrophilic' when water is the solvent.

  • Examples of lyophilic colloidal systems include foams, milk, and smoke (liquid in gas, liquid/liquid emulsion, solid in gas).

Properties of Colloids - Kinetic

  • Kinetic properties relate to the motion of colloidal particles.
  • Interactions between particles can lead to aggregation or coalescence (if liquid droplets) and destroy the colloidal system.
  • Brownian motion describes random collisions between particles in a liquid (or gas) dispersion medium. This results in particles travelling in a zig-zag fashion.
  • Stokes' Law describes the velocity of sedimentation (or creaming) for spherical particles falling through a liquid: V = 2r²g(σ-ρ)/9η, where:
  • V = velocity of sedimentation/creaming
  • r = radius of particle
  • g = acceleration due to gravity
  • σ = density of particle
  • ρ = density of liquid
  • η = dynamic viscosity of liquid
  • Reducing sedimentation velocity involves reducing particle size, increasing the viscosity of the continuous phase, or decreasing the density difference between the phases.
  • Examples of applications affecting sedimentation velocity include producing smaller particles, increasing viscosity of the surrounding liquid, decreasing the density difference between the particle and the medium.

Diffusion

  • Colloidal particles spontaneously diffuse from higher concentration regions to lower concentration regions.
  • Fick's first law describes the rate of diffusion. dm/dt = -DA dC/dx where:
  • dm/dt = mass of substance diffusing per unit time
  • D = diffusion coefficient
  • A = area across which diffusion occurs
  • dC/dx = concentration gradient

Pharmaceutical Suspensions

  • Suspensions are dispersions of insoluble drugs in a continuous liquid phase (aqueous or non-aqueous).
  • Colloidal or slightly coarser particles are used, with gravity having a significant impact.
  • The advantages of suspensions include overcoming difficulties in swallowing solid dosage forms and maintaining drug stability (e.g., preventing hydrolysis).
  • Taste and high surface area are also inherent properties of suspensions.
  • Common problems associated with suspensions include sedimentation, caking, flocculation, and particle growth (including recrystallization).

Types of Suspensions

  • Classified by dispersion medium (aqueous or oily), formulation type (flocculated or deflocculated), and drug stability (ready-to-use or reconstituted powders).
  • Common uses include oral, parenteral, topical, ocular, and x-ray contrast media formulations.

Formulation of Suspensions

  • Practice involves avoiding aggregation/caking, adhesion of particles to vessel surfaces, and creating a flocculated system (loose assembly of particles).
  • Ideal suspensions are partially, not fully, flocculated.
  • Fully flocculated systems exhibit a clear supernatant, large sediment volumes, rapid sedimentation, and easy redispersal.

Electrical Properties of Colloids

  • Most colloidal particles dispersed in water possess a surface charge due to ionisation or adsorption.

  • This charge affects the distribution of ions in the medium. A layer of counterions, and then co-ions build up a double layer adjacent to the particles. Zeta potential reflects this charge build up.

  • Zeta potential: a measure of the electrical potential at the shear plane.

  • A value above ±30 mV usually indicates sufficient repulsion to prevent particle aggregation and ensure colloidal stability.

  • Changes in zeta potential can be used to predict stability with the addition of surfactants and electrolytes.

Modification of zeta potential

  • Zeta potential modification can impact suspension stability and is affected by various factors including the presence of ions like electrolytes and the presence of surfactants.

Quality Control of Suspensions

  • Quality control aspects include physical appearance, particle size analysis, ease of redispersal, sedimentation volume ratio, zeta potential, rheology (shear thinning/thixotropy is favorable).

Other Important Concepts

  • Size reduction: Coarse suspensions (>1 µm) requiring size reduction (e.g., to avoid grit, prevent issues with hypodermic needles, and improve drug release/bioavailability).

  • Surfactants: Used for wetting (interfacial tension reduction), controlling flocculation through various mechanisms of charge and interactions.

  • Electrolytes: Modification of zeta potential through modifying the charge on the particle, and sometimes used to control flocculation/aggregation depending on ionic valence (Schultz-Hardy rule).

  • Thickening agents: Used (e.g., Acacia, starch, hydroxypropylcellulose, and carmellose sodium) to modify the viscosity of the suspension vehicle.

  • Schultz-Hardy rule: The ability of an electrolyte to induce flocculation/aggregation depends on the valence of the ions. Trivalent > divalent > monovalent ions.

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MPharm Programme Colloids & Suspensions PDF

Description

Test your knowledge on pharmaceutical suspensions, including their characteristics, advantages over solid dosage forms, and the behavior of particles in flocculated and deflocculated systems. This quiz covers key features of colloidal systems and their stability.

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