3. ADSORPTION
• Adsorption is the adhesion of atoms, ions or
molecules from a gas, liquid or dissolved solid to a
surface
4. Adsorption: Solid/vapour systems
• If a gas or vapour comes into contact with a solid, some of it
will become attached to the surface
• This reduces the imbalance of attractive forces and hence the
surface free energy
• The term sorption is used in this case
• Adsorption may be by relatively weak non-specific forces (van
der Waals forces) and is termed physical adsorption
• Alternatively, the adsorption may be by stronger specific
valence forces and is called chemisorption
5. • Physical adsorption is rapid and reversible and multilayer
adsorption is possible
• Chemisorption is specific, may require activation energy,
and therefore be slow and not readily reversible
• Only monomolecular chemisorbed layers are possible
6. Adsorption: Solid/liquid systems
• Adsorption of most interest is that of a solute, in solution,
onto a solid
• Adsorption from solution: Several factors affect adsorption
from solution:
• Solute concentration: increase in concentrate of solute will
cause an increase in the amount of adsorption
• Temperature: Adsorption is generally exothermic and hence
an increase in temperature leads to a decrease in
adsorption
7. • pH: Influence of pH is usually through a change in ionization of
the solute
• the influence will depend on which species is more adsorbed
• Surface area of adsorbent: An increase in surface area, will
increase the extent of adsorption
• Increase in surface area can be achieved by a reduction in
particle size or the use of a porous material
8. Pharmaceutical applications of adsorption from solution
• Chromatographic techniques and removal of
unwanted impurities
• Adsorption of poisons/toxins
• The ‘universal antidote’ for use in reducing the
effects of poisoning by the oral route is composed of
activated charcoal, magnesium oxide and tannic acid
9. • A more recent use of adsorbents has been in dialysis
to reduce toxic concentrations of drugs by passing
blood through a haemodialysis membrane over
charcoal and other adsorbents
• Taste masking
• Drugs such as diazepam may be adsorbed onto solid
substrates to minimise taste problems,
10. Applications of adsorption
• Haemoperfusion
• Carbon haemoperfusion is method of treating cases of severe
drug overdoses and originally involved perfusion of the blood
directly over charcoal granules
• Activated charcoal granules are very effective in adsorbing
many toxic materials,
• but they give off embolising particles and also lead to removal
of blood Platelets
• These problems are removed by microencapsulation of
activated charcoal granules by coating with biocompatible
membranes such as acrylic hydrogels
11. • Adsorption in drug formulation
• Beneficial uses include adsorption of surfactants and polymers in
the stabilisation of suspensions,
• and adsorption of surfactants onto poorly soluble solids to
increase their dissolution rate through increased wetting
• Problems may arise from the adsorption of medicaments by
adsorbents such as antacids, which may be taken simultaneously
by the patient, or which may be present in the same formulation
• and from the adsorption of medicaments on to the container
walls, which may affect the potency and possibly the stability of
the product
12. Disadvantages of adsorption
• Adsorption may cause problems in formulation
where drugs or other materials such as preservatives
are adsorbed by containers
• Certain additives such as parabens may be adsorbed
onto the solid material present in a suspension,
leading to a loss in antimicrobial activity
• Glyceryl trinitrate is a volatile solid given in the form
of tablets
13. • The vapour may be sorbed by the container leading
to further volatilization and loss of potency
• The adsorption of insulin onto the intravenous sets
• the sorption of phenylmercuric acetate, used as a
preservative in the eye drops, on to polyethylene
containers
16. Define the following terms:
[Adsorption, chemisorption, adsorbent, mask, Haemoperfusion, etc]
Respond to the following questions:
Give a detailed account of adsorption process
Explain in details the process of adsorption between solid and vapour phases with
examples
Explain in details the process of adsorption between solid and liquid phases with
examples
With examples, pharmaceutical applications of adsorption process
17. Group work discussional questions:
Explain in details the process of adsorption between solid and
vapour phases with examples
Explain in details the process of adsorption between solid and
liquid phases with examples
With examples, pharmaceutical applications of adsorption
process
