Heat

• Scanned with CamScanner
• Convection involves the movement of heated air or liquid, such as hot water rising in a kettle or warm air moving upwards in a room.
• Pharmaceutics


  The scientific and technological aspects of the design and manufacture of dosage forms
• Medicines


  Drug delivery systems - means of administering drugs to the body in a safe, efficient, reproducible and convenient manner
• Pharmaceutics converts a drug into medicine
• Solid state


  One of the three states of matter, defined in thermodynamic terms as a state of matter that is uniform throughout in chemical composition and physical state
• Solids


  • The physical form (packing of molecules and size/shape of particles) can influence how the material behaves
  • At normal room temperature and pressure, the majority of drugs and excipients exist as solids, so the study of solid systems is of enormous pharmaceutical importance
  • The solid state is the dominant means of presentation of a drug
• Powder


  A collection of small discrete solid particles in close contact with each other, with the void space usually filled with gas
• Powder technology


  The foundation of dosage form design, as in 90% of medicines the active ingredient is in the form of solid particles
• Powder science


  The understanding of particulate materials at a molecular level, their behaviour as individual particles, and the physical and mechanical properties of collections of particles under defined conditions or in specific processes
• Powder properties


  • Fundamental properties (size, size distribution, shape, porosity, true density, surface area)
  • Derived properties (adhesion, flow, compressibility)
• Particle size


  The diameter of a sphere equivalent to the particle in weight, volume, surface area, projected area or sedimentation velocity
• Particle size distribution


  The range of particle sizes in a group and the distribution of the sizes within the range
• Monosized particle population


  A population consisting of spheres or equivalent spheres of the same diameter
• Most powders contain particles with a range of different equivalent diameters
• Powder flow properties


  The resistance to differential movement between particles, affected by interparticle forces like electrostatic attraction, Van der Waals forces, and moisture-related forces
• Generally, particles greater than 250 μm are free-flowing, particles smaller than 100 μm have reduced flow
• Factors affecting powder flow

  • Particle size, shape, porosity, density and surface texture
  • Particle density affects flow through its influence on the relative contributions of gravity and surface forces
  • Surface roughness affects flow due to its influence on particle adhesion
  • Moisture adsorption can improve flow by pore-filling, increased density and lubrication, but capillary forces can reduce flow
• Methods of measuring powder flow

  • Static bed methods (angle of repose, angle of spatula, compressibility index, Hausner's ratio, shear cell measurement)
  • Dynamic methods (rotating powder drum, vibrating spatula)
• Angle of repose


  The angle that the surface of the cone of powder makes with the horizontal surface, indicating ease of flow (small angles <30° = free flowing, large angles >50° = poor flow)
• Angle of spatula


  The angle of powder remaining on a spatula that has been vertically removed from a powder bed, similar to angle of repose
• Carr's compressibility index (CI)

  Calculated as (tapped density - bulk density) / bulk density x 100%, indicating flow properties (CI >20% = poor flow)
• Hausner's ratio (HR)


  Calculated as tapped density / bulk density, indicating flow properties (HR ~1.2 for free flowing, ~1.6 for cohesive powders)
• Hopper flow rate


  The rate at which powder discharges from a hopper, a direct measure of powder flowability
• Uniform powder feed and flow is important for maintaining tablet weight uniformity and preventing issues like capping or lamination in high-speed tableting
• Particle size analysis


  Obtaining quantitative data on the size, distribution, and shapes of drug and other components in pharmaceutical formulations
• Sieving


  Placing powder in a stack of sieves with increasing aperture size, agitating, and weighing the contents of each sieve to determine the particle size distribution
• Limitations of sieving include particle aggregation, shape effects, and blockage of apertures
• Microscope methods


  Directly measuring and counting particles using an optical microscope, but limited by factors like particle shape, position, and aggregation
• Conductivity methods


  Using a Coulter counter to measure particle size based on changes in electrical conductivity as particles pass through an aperture
• The use of a microscope to examine and measure particles is a very effective procedure for particle size analysis, as it is the only method in which a direct measurement of the particle is made with optical microscope
• Samples prepared for light microscopy must be adequately dispersed on a microscope slide to avoid analysis of agglomerated particle
• This involves counting not fewer than 200 particles in a sample using a calibrated eyepiece on a microscope
• Particle size range


  • 10 - 20
  • 21 - 30
  • 31 - 40
  • 41 -50
• Mean (X)


  • 15
  • 25.5
  • 35.5
  • 45.5
• Freq (F)


  • 15
  • 45
  • 25
  • 15
• FX


  • 225
  • 1147.5
  • 887.5
  • 682.5
• Average diameter = ƩFx/ƩF = 2942.5/100 =29.425
• Disadvantages of this method include the shape, particle position, aggregation, speed of method and sampling
• Coulter counter is one of the more recent particle size analysis procedures to be developed