PHARMACEUTICS GPAT SHORT NOTES II

1. What is Draves test?

Draves test is used for measuring the efficacy of wetting agent.
Procedure: In this test, 5 gm cotton skein is attached to a 3 gm hook, which is tied by means of a thread to a weight. The skein is placed into a cylinder containing the surfactant solution to be tested and is held submerged by the hook and the thread is attached to the weight.  As soon as most of the air is displaced by the liquid, the skein sinks to the bottom. The shorter the sinking time, the better the wetting agent. The gray cotton skein used for this purpose contains natural waxes and oil that make it hydrophobic and wetting is not instantaneous, hence the test measures the rate of wetting.

2. General terms of solubility phenomenon
There are four general terms used to define solubility of system viz. Cosolvency, solubilization, complexation and hydrotrophy.
a) Cosolvency: It is the phenomenon of increasing the solubility of weak electrolytes and non-polar molecules by addition of a water miscible solvent in which the drug has good solubility. 
E.g. ethanol, sorbitol, glycerin, propylene glycol, polyethylene glycols are used as co-solvents in oral preparations. 
Dimethylacetamide is used as co-solvents in parenteral products.
b) Solubilization: Solubilization is the spontaneous passage of poorly water-soluble solute molecules into an aqueous solution of a soap or a detergent in which a thermodynamically stable solution is formed. Solubilising agents generally have HLB values higher than 15. 
E.g. Polyoxyethylene sorbitan fatty acid esters (Tween series), polyoxyethylene monoalkyl ether (BRIJ and MYRJ series) and sucrose monoesters, lanolin esters and others.
c) Complexation: The increase in solubility of a drug can be achieved by forming an association or complex with complexing agents.
E.g. Polyvinyl pyrrolidone is used to increase solubility of iodine. Beta cyclodextrins are used to enhance solubility of various drugs.
d) Hydrotrophy: It means the increase in solubility of a solute in water due to presence of large amount of additives.
E.g. Solubilization of benzoic acid with sodium acetate, sodium glycinate. Solubilization of adrenochrome monocarbazone with sodium salicylates.

3. Which methods are used for determination of particle size?

- Sieving method

- Microscopy

- Sedimentation

- Electrical conductivity method

- Light and X-Ray scattering

4. What is milling?

- Milling is a mechanical process employed for reduction of particle size of the solids. 

- It includes the terms like grinding, pulverization, crushing, dispersion, etc.

- The size of the solid particles is expressed in mesh size i.e. numbers of the pores per inch of the screen.

Coarse milling produces particles of size : 20 mesh.

Intermediate milling: 20-200 mesh.

Fine milling: > 200 mesh.

5. Relationship between particle size in microns and mesh size of sieve.

PS(micron) : Mesh size

        2000     :  10

          850     :  20

          600     :  30

          400     :  40

          300     :  50

          250     :  60

          200     :  70

          175     :  80

          150     :  100

            75     :  200

            37     :  400

6. The most commonly used mills for size reduction.

i) Hammer mill : for almost all the drugs

ii) Roller attrition : for soft materials

iii) Fluid energy mill : moderately hard and friable materials

iv) Cutter mill : Fibrous materials

v) Colloid mill : emulsions

vi) Ball mill: Hard materials

Impact and attrition: Ball mill, fluid energy mill.

Impact: Hammer mill

Stress and attrition: Roller attrition mill

Cutting and shearing: Cutter mill

Hammer mill is generally used for wet granulation.

Colloid mill is used for size reduction of globules in an emulsion (2000 to 20000 rpm)  and not used for dry materials.

Ball mill is a closed system. It contains the amount of balls 50% of the the mill volume. Size of the balls is decided as per the required particle size of material. It is operated at 60-85% critical speed. Due to its closed structure toxic materials can be milled in this equipment.

7. Purpose of drying

i) to minimize bacterial growth

ii) to improve chemical stability

iii) increase in stability of overall system

8. Non- thermal methods of drying

i) Adsorption of water from solvent by using desiccants.

ii) Absorption of moisture from gases by passing through H2SO4 acid column.

iii) Extraction of liquid from solid using a solvent.

iv) Squeezing.

9. Hygroscopic: Natural tendency to absorb moisture. e.g. glycerin, absolute alcohol.

10. Deliquescent: Natural tendency to absorb water and liquify e.g. Calcium chloride.

11. Efflorescent: Natural tendency to loose moisture e.g. borax, caffeine.

12. Micelles: Micelle is an aggregate of surfactant molecules dispersed in a liquid colloid.

13. Critical Micelle Concentration (CMC): it is the concentration of surfactant above which micelles are spontaneously formed.

14. Krafft temperature: It is also known as Krafft point or critical micelle temperature. It is the minimum temperature at which surfactants form micelles.