Pharmacuetical Aquametry Flashcards
In what ways is water present in drug formulations?
*solvent or diluent
*absorbed (unbound) - hygroscopic substances
*water of crystallisation
Why is the study of water content in drugs important?
If above specified amount-
*enhanced degradation by hydrolysis
*facilitates growth of organisms
*increases weight- issues with batch calculations
*impaired stability of end product
What is efflorescence?
The loss of water of crystallisation from a substance to the atmosphere on exposure to air
If substance has higher concn of water - moves out
Loss continues until equilibrium reached
How can efflorescence be prevented?
*close container tightly immediately after use
*fill container completely- use of fillers
What is hygroscopy?
The ability of a substance to attract and hold water molecules from surrounding atmosphere by absorption or adsorption.
Material now physically changed- increased volume, stickiness
*if absorbs enough water, can dissolve in it - deliquescence
What is exsiccation?
Removing water of crystallisation by HEATING.
Heat applied until desired weight obtained or calculated loss obtained
Bcuz anhydrous substance may be required
How is water content determined?
*drying methods- ovens, infrared lamps and infrared balances DISADVANTAGE- loss on drying determined-not necessarily water content
*distillation- DISTILLATION- large samples required, time consuming
*titration methods- Karl Fischer Titration- ADVANTAGES- rapid, specific for water. Small sample size - DISADVANTAGE- substances may react with iodine or iodide
How is water quantified in KFT?
Water and iodine consumed in a 1:1 ratio- if we know iodine, we know water
What two types of KFT are there?
*volumetric- based on volume of KFT reagent consumed
*coulometric- no titrant added - iodine generated in situ
