W5 Disperse systems- Dosage forms Flashcards
What is a colloid/colloidal dispersion?
A two phase system of matter; a type of mixture intermediate between homogenous and heterogenous mixtures. (size <1 micron)
What is a phase colloid?
Small droplets or particles of one substance are dispersed in another
What is a molecular colloid?
Macromolecules are dispersed in a continuous phase
What is a disperse system?
One phase is distributed throughout a second phase
( a continuous phase or dispersant)
(two immiscible phases in contact)
What is electrophoresis?
Migration of charged particles
Surface dependent
What is thixotropy?
Exhibits stable form at rest
Becomes fluid with shear/agitated
E.g. paint
What does lyophobic and lyophilic mean?
Solvent hating (hydrophobic)
Solvent liking (hydrophilic)
(lyo means solvent)
Calcium phosphate (in toothpaste) is lyophobic or lyophilic?
Lyophobic
Starch and gelatine are lyophobic or lyophilic?
Lyophilic
What is a sol?
examples?
A colloidal suspension of small, solid particles in a continuous liquid medium e.g. paint, mud
(solid in a liquid)
What is a gel?
A colloidal suspension in which the liquid medium has become viscous enough to behave more or less as a solid.
How can you identify if a gel is a two phase system? (lyophobic)
Flocculated particles in a two-phase gel
Network of elongated particles or rods forming a gel structure
(particles are attached)
Usually opaque, not as stable as single phase
How can you identify if a gel is a one phase system? (lyophilic)
Matted fibres as found in soap
Crystalline and amorphous regions in a gel of carboxymethylcellulose
Clear or translucent, with no definite boundaries between the dispersed macromolecules and the liquid.
Can be dispersed in water to provide a range of bases from mobile liquids to solids
What are foams?
how are they formed?
- Gases dispersed in a liquid/solid
- Formed by trapping many gas bubbles
What instruction is given for most liquid dosage forms
‘Shake well before use’
Types of defoamer/antifoaming agents
How do they work?
Foam breakers and preventers
- Act as small droplets forming in the foam lamellae
- Displaces surfactants at the air-water interface
e.g. silicone fluids
What type of emulsion is cod liver oil?
An oil in water dispersion
Is a suspension a colloid?
No.
As they are generally larger than 1 micron/micrometer
What are suspensions?
Insoluble particles are dispersed within a liquid medium which is usually aqueous
e.g. ibuprofen or paracetamol oral suspension
Which is bigger?
Suspension, Colloid or Solution?
Suspension.
What are the properties of colloids?
Tyndall effect
Brownian motion
Adsorption
Dialysis
Electrophoresis
Thixotropy
What is an emulsion?
A liquid in a liquid e.g. a cream
What is a foam?
A gas in a liquid
What happens when dissolving a solute into a solvent? (6)
Molecular dispersion
Contains small particles (ions or molecules)
Transparent
Do not separate
Cannot be filtered
Do not scatter light
What are 3 examples of everydaysolutions?
Saline solution
Multi-purpose contact lens solution
Hydrogen peroxide contact lens solution
Makeup toner
What are 3 examples of disperse systems?
Droplets of pine oil dissolved in active germ killing ingredient
Face cream
Nail polish
What is an example of a pharmaceutical solution?
Mouth wash (Chlorhexidine gluconate)
Feminine wash
Saline laxative (constipation relief)
What are examples of pharmaceutical disperse systems?
Amoxicillin oral suspensions
Aveeno lotion
Pfizer solution
What is the Tyndall effect?
Colloids scatter light
(light beam path through colloid is visible due to light scatter)
What is Brownian motion?
Under a microscope, the molecules of the liquid are in motion
Because of the motion, the larger particles of the colloid are being constantly bombarded by the smaller particles of the liquid
What is adsorption?
A chemical is associated to the surface of a second agent
Often reversible
Can lead to conformational changes
Manipulate physiochemical properties
What is dialysis? (in colloids)
Separation of suspended colloidal particles from dissolved ions or molecules of small dimensions
By means of their unequal rates of diffusion through the pores of semi-permeable membranes
What is the formulation (ingredients) of gels?
Gelling agents, semisynthetic materials, synthetic, humectants, preservatives, water
Why can foams pose as a problem?
The foam forms on shaking and might be too much so a defoamer should be added
