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INTRODUCTION Almost all drugs are marketed as tablets, capsules or both or as an injection. Prior to their development, physical and chemical properties of the drug molecule and other derived properties of the drug powder are determined.


SPECTROSCOPY Most drugs absorb light in the UV wavelengths (190-300nm ). The acidic or basic nature of the molecule can be predicted from functional groups. Using the UV spectrum of the drug, an analytical wavelength suitable to quantify the amount of drug in particular solution can be chosen.


SOLUBILITY D etermination of pK a , temperature dependence, pH solubility profile, solubility products, solubilisation mechanisms and rate of dissolution . pK a Determination For acidic compounds: pH = pK a + log [ ionized drug] [unionized drug] For basic compounds : pH = pK a + log [un ionized drug ] [ionized drug]

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Intrinsic solubility The maximum amount of solute dissolved in a given solvent under standard conditions of temperature, pressure and pH. Salts A major improvement in solubility, achieved by forming a salt. Solvents Water soluble solvents - improve the solubility. Oils - emulsions, topicals , intramuscular injections and liquid fill oral preparations.

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Aqueous methanol - in HPLC. Non aqueous solvent acceptable - glycerol , propylene glycol and ethanol.


MELTING POINT 1. Capillary melting 2. Hot stage microscopy 3. Differential scanning calorimetry or thermal analysis POLYMORPHISM A solid material with at least two different molecular arrangements that give distinct crystal species. These differences disappear in the liquid or the vapour state

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Pseudopolymorphism ( solvates) The crystalline form of a drug can either be a polymorph or a molecular adduct or both. The stoichiometric type of adducts where the solvent molecules are incorporated in the crystal lattice of the solid are called as solvates, and the trapped solvent as solvent of crystallization. The solvates can exist in different crystalline forms called as pseudopolymorphs . ( Pseudopolymorphism)

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ASSAY DEVELOPMENT TLC is widely used in a semiquantitative mode to estimate impurity levels, to establish the number of impurities. HPLC is now acknowledged as the most versatile and powerful technique in pharmaceutical analysis. THIN LAYER CHROMATOGRAPHY For the separation of complex mixtures in stability samples . Will quantify the number of components and estimate their concentration by reference to standards

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HIGH PERFORMANCE LIQUID CHROMATOGRAPHY T he column can be much smaller and use much smaller particle size packing material (stationary phase). Shorter retention times, high sensitivity.


MICROSCOPY Two major applications: Basic crystallography, to determine crystal morphology, polymorphism and solvates. Particle size analysis. CRYSTAL MORPHOLOGY Cubic , tetragonal, orthorhombic, monoclinic, triclinic and hexagonal with different internal structures and spatial arrangements. Crystals can adopt different external structures – crystal habit. Crystal habit modified by excessive supersaturation , cooling rate and agitation, addition of cosolvents .

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PARTICLE SIZE ANALYSIS Sieving For small quantities - Microscope The Coulter Counter Method Laser light scattering

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POWDER FLOW PROPERTIES The flow of the powder can be evaluated by measurements of bulk density and angle of repose. BULK DENSITY Carr ’ s index (%) = Tapped – poured density ͯ 100 Tapped density

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ANGLE OF REPOSE By the action of gravity One limitation exists: the angle to horizontal cannot exceed a certain value - angle of repose (ϴ ). If any particle temporarily lies outside this limiting angle, it will slide down the adjacent surface under the influence of gravity until the gravitational pull is balance by the friction caused by interparticulate forces.

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