Laboratory Revision

Question 1

What is a polymorph?

Answer 1

A compound that can crystalline in different forms.

Question 2

What is a solvate/Hydrate?

Answer 2

A compound formed by the interaction of a solvent and a solute. The crystal lattice contains a solvent.

Question 3

Apart from the three states of matter being gas, liquid and solid what is the 4th state that lies between a liquid and a solid?

Answer 3

Liquid crystalline state

Question 4

What can liquid crystals be divided into?

Answer 4

Lyotropic, Thermotropic and metallotropic liquid crystals.

Question 5

What is Anisotropy?

Answer 5

A difference in physical property (absorbance, optical property, density, etc when measured along different axes.

Question 6

What is birefringence?

Answer 6

Birefringence (dual refraction) is an optical property in which a single ray of plane polarised light entering an anisotropic material splits into 2 Ray’s, travelling at different speeds and different directions (2 refractive indices).

Question 7

Define Isotropy

Answer 7

The optical properties is identical in all directions (one refractive index-singly refracting)

Question 8

What type of surfactant is Sodium Lauryl Sulfate (SLS)?

Answer 8

It is an anionic surfactant, the hydrophilic head consists of a negatively charged sulphate group.

Question 9

Chemical degradation may result in…?

Answer 9

Altered efficacy and toxicological consequences.

Question 10

What are the main chemical reactions that affect stability of a drug?

Answer 10

Oxidation and hydrolysis

Question 11

Why is the ASA hydrolysis study carried out in buffered solution?

Answer 11

So that hydroxyl ion concentration remains essentially constant

Question 12

What order of reaction is the hydrolysis of Aspirin?

Answer 12

It is a first order reaction, The reaction is dependent on the concentration of aspirin. Therefore the degradation of aspirin in a buffered solution will follow first order kinetics 1st order rate processes are by far the most important kinetic order involved in pharmaceutical processes.

Question 13

What is the effect of pH on aspirin hydrolysis?

Answer 13

If pH is greater than 9 it will be rapid hydrolysis.

Question 14

What is the effect of temperature on aspirin hydrolysis?

Answer 14

Increasing temperature will increase the reaction rate and there is an increase in degradation (hydrolysis)

Question 15

What is shelf life?

Answer 15

It is the length of time required for the product potency to be reduced to some percentage of its original value. For most products this is the t90 or time at which the product retains 90% of its original potency.

Question 16

Why are stability studies done at elevated temperatures?

Answer 16

It allows for faster prediction of the shelf life as stability tests at room temperature would take a long time as a screening procedure for new formulations.

Question 17

What is half life?

Answer 17

It is the length of time required for the concentration of a drug to drop by 50%

Question 18

What is a buffered solution?

Answer 18

An aqueous solution consisting of a mixture of a
-weak acid and its conjugate base
-weak base and its conjugate acid
It’s pH changes very little when small quantities of strong acid for base are added to it, therefore it is used to prevent changes in the pH of a solution.

Question 19

What is surface tension?

Answer 19

Within a liquid molecules attract each other equally in all directions. At the surface there is no force attracting them outwards so the molecules are pulled towards the interior of the liquid. The exposed surface tends to contract to the smallest possible area because of unequal molecularly cohesive forces near the surface. Therefore surface tension is the elastic tendency of liquids which makes them acquire the least surface area possible. Surface tension is responsible for the shape of liquid droplets.

Question 20

What is the effect of NaCl on the CMC of SLS?

Answer 20

SLS is very sensitive to the polarity of the medium. The CMC decreases as the ionic strength is increased. Na ions interact wit the - charge on the sulphate group reducing the electrostatic repulsion between like - charged head groups and so lower the CMC.

Question 21

What are other factors affecting CMC?

Answer 21

Electrolyte addition to solutions of ionic surfactants decreases CMC.
Increase the length of the hydrocarbon chain makes the molecule more hydrophobic/lipophilic and decreases CMC.
Increase in the ethylene oxide chain length of a non-ionic surfactant makes the molecule more hydrophilic increasing CMC.

Question 22

What is the importance of CMC?

Answer 22

The lower the CMC the less surfactant required for emulsification and solubilisation Ionic surfactants generally have higher CMC than non-ionic surfactants.

Question 23

What are pharmaceutical applications of surfactants?

Answer 23

1: Solubilising agent when their conc reaches CMC the ability to solubilise lipophilic drugs (e.g. Steroids and water insoluble vitamins) to allow it to dissolve in water.
It is the process whereby water insoluble substances are brought into solution by incorporation into micelles.
2:Topical applications They are potent permeation enhancers because of their ability to solubilise lipids, they increase drug absorption across biological membranes.
3: As antimicrobial agents against gram + and gram - organisms.
Used as a bactericide for the destruction of cell walls. The solubilisation of phenolic compounds e.g. Creosol and chlorocresol with soap to form clear solutions for use in disinfection. Solubilised solution of iodine in non-ionic surfactant for use in instruments sterilisation.