Pharmaceutics Revision Flashcards
Name 3 co-solvents
Glycerol, Propylene glycol, Ethanol
How big are the particles found in solution?
Less than 1nm
How small are colloids?
Between 1nm and 1micrometer
How big are suspension particles?
Between 1micrometer and 1mm
What are some ways to test for a colloidal system?
Using light, colloids cause Tyndall scattering
What makes a disperse system?
There are two phases, a continuous and disperse phase
What is Brownian motion of a colloid?
Brownian motion is the constant bombardment of smaller particles onto the bigger ones which cause them to stay suspended.
What are the two types of colloids?
Lyophilic and lyophobic (loving or hating the solvent, which ever one it is determines if it will be a two phase or one phase system)
What is creaming?
Density differences between the oil and water cause the droplets to concentrate at the top of the system
What is flocculation?
When two particles aggregate together (can be reversed by shaking)
What is coalescence?
When two particles collide and form one larger droplet (cannot be undone)
What is Ostwald ripening?
Particles collide and cause each other to grow or shrink. This continues and then there are many large particles and small particles. Eventually the small particles separate at the top
Describe the second trough of the DVLO graph
It is known as the secondary minimum and is caused by flocculation. The attractive forces are weak and can be reversed
Describe the main peak in the DVLO graph
Known as the primary maximum, it is the point where particles experience the most repulsion. The peak of this wave is known as Vmax and it determines the stability of the system
Describe the main trough in the DVLO graph
It is known as the primary minimum and this is the point where particles coagulate irreversibly
The DVLO only applies to ionic surfactants
How do non ionic surfactants work?
Steric effects - polymers overlap which reduces energy and thus being unfavourable for the molecule so causes repulsion
Osmotic force - when polymers overlap there is less water in that space so water will move from high to low concentrations and push them apart
What is sedimentation?
The process of particles settling
What is the use of co-solvents?
Enhance the solubility of poorly soluble drugs
What is the use of antioxidants like sodium sulphite?
Enhance the stability of chemical agents which are prone to oxidation. They exhibit higher oxidative potential so basically oxidise before the drug molecule.
What is the use of preservatives like benzoic acid?
They control the microbial bio burden of the formulation
