colloid & suspension
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What is the outcome of particles in a deflocculated suspension?

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

    • 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.</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</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.</p> Signup and view all the answers

    When classifying suspensions, which factor is NOT considered?

    <p>Rate of particle growth</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.</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.</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.</p> Signup and view all the answers

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

    <p>Oily phases</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.</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.</p> Signup and view all the answers

    What distinguishes lyophilic colloids from lyophobic colloids?

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

    What does a colloidal system primarily use for drug delivery?

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

    Which of the following systems can be classified as colloids?

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

    What defines a colloidal solution when water is the solvent?

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

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

    <p>Milk</p> Signup and view all the answers

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

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

    How does Brownian motion influence colloidal systems?

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

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

    <p>Xanthan gum</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.</p> Signup and view all the answers

    What is the formula for calculating the sedimentation volume ratio?

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

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

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

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

    <p>Acacia</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.</p> Signup and view all the answers

    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

    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.

    • 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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