Pharm Aquametry Flashcards
Define aquametry.
Analytical process to measure the water present in a substance or product.
What can happen if pharm substances contains more than the specified/accepted amount of water? (6)
- Enhances degradation of drug by hydrolysis.
- Facilitates growth of microorganisms - spoilage.
- Increases weight of substance complicating batch/formulation calculation.
- Physical properties modified by H2O content.
- Process such as granulation, tableting and coating affected.
- Impairs stability.
What is water of crystallisation?
- molecular mass is affected by water of crystallisation.
Water that is stoichiometrically (chemically) bound within the crystal but can dissociate by heating.
What 4 processes influence the hydration of a pharmaceutical product?
Efflorescence
Hygroscopy
Deliquescence
Exsiccation
What is efflorescence?
The loss of water of crystallisation to the atmosphere on exposure to air.
- depends on vapour pressure.
How can efflorescence be prevented?
By closing the container tightly immediately after use and filling the container completely so there is no space for air.
What is hygroscopy?
The ability of a substance to attract and hold water molecules from the surrounding atmosphere by absorption or adsorption.
Describe how deliquescence works.
If the material is very hygroscopic, it may absorb enough water from the atmosphere to dissolve in this water in a process called deliquescence.
Material = deliquescent.
What is exsiccation?
The process of removing water of crystallisation by heating.
Heat is applied until a constant weight is obtained or the calculated loss in weight has taken place.
What are the 3 methods used to measure the water content in pharmaceutical product?
- Drying methods - drying ovens, IR lamps and IR balances.
- Distillation.
- Titrations - KF titrations.
What is the disadvantage of using drying methods such as ovens to determine the water content of a product?
Loss on drying is determined but not necessarily water content - if containing volatile substances they will be lost.
Time consuming process.
What is the disadvantage of using distillation as a method to determine water content?
Large samples required.
Unsuitable for trace amounts of water.
Time consuming.
What is the advantage of using KF titration in determining water content?
Rapid and specific for water.
Small sample size required.
Method can be validated and fully documented.
What is the disadvantage of using KF titration in determining water content?
Substances which react with iodine/iodide can interfere with the reaction e.g. ascorbic acid and quinine.
In what two ways are titration end points detected?
Indicators - phenylphthalein, methyl-orange.
Electrometrically - conductivity, amperometry, potentiometry, voltammetry.
(Others: spectroscopy, calorimetry, pH, precipitation).
What is the equivalence point in titration reactions?
Stoichiometrically equivalent amounts of titrant and titrand have reacted and reaction is complete.
- Theoretical end point.
What is the end point of a titration reaction?
End point is what is actually measured by indicator or instrumentation.
Is different to equivalence point and there is indicator error.
Where does the water come from if the KF reagent is anhydrous?
From the sample itself.
Sample must contain water for reaction to occur.
What are the two types of KF titrations called?
Volumetric
Coulometric
Describe how the loss on drying process works?
Measure high moisture content in solid/semi-solid materials.
Drying is carried out over potent dehydrating agent = diphosphorus pentoxide granules.
LOD calculated as percentage.
Sample is weighed, dried and reweighed.
Why are anhydrous substances sometimes required for certain pharmaceutical formulations?
Reduces bulk and weight of the drug substance/excipient.
Explain how vapour pressure works in terms of loss of water into atmosphere etc.
If vapour pressure of the hydrated substance is greater than the vapour pressure of the atmosphere, then the hydrated substance will lose water to the atmosphere and become less hydrous.
The loss of water will continue until equilibrium has been reached between the hydrated substance and atmosphere.
What is the gold standard method of detection in KFT?
Amperometry
Is LOD method suitable for all pharma products?
Not suitable for pharmaceutical products containing other volatile substances.
