Explain the principles of extraction in chemistry and list the ideal properties of an extraction solvent.

a) Extraction is a process that separates a specific component from a mixture by dissolving it in a solvent that is selective for that component.

The theory of extraction relies on the differential solubility of a substance in two immiscible phases. When a solute is exposed to two immiscible solvents, it distributes itself between them based on its relative solubility in each. This distribution is quantified by the partition coefficient ($K_D$), which is the ratio of the solute's concentration in the extracting solvent to its concentration in the original phase:

$$K_D = \frac{\text{Concentration of solute in extracting solvent}}{\text{Concentration of solute in original phase}}$$

An effective extraction uses a solvent where the desired component has a high $K_D$, moving it efficiently from the original mixture into the new solvent.

b) Ideal properties for extraction solvents include:

• Selectivity: It should dissolve only the target compound, leaving impurities behind.
• High solvent power: It should be able to dissolve a significant amount of the desired substance.
• Immiscibility: It should not mix with the original phase to allow for easy separation.
• Ease of recovery: The solvent should be easily removed from the extracted compound (e.g., by evaporation).
• Chemical inertness: It should not react with the solute or other components in the mixture.
• Safety: It should be non-toxic, non-flammable, and environmentally friendly.
• Cost-effectiveness: It should be inexpensive and readily available.
• Physical properties: Low viscosity and surface tension to aid mass transfer and phase separation.

a) Pharmaceutical applications of Filtration as a unit operation include:

• Clarification: Removing suspended particles from liquid formulations like syrups, eye drops, and injectables to ensure clarity and patient safety.
• Sterilization: Using membrane filters with very small pore sizes (e.g., $0.22 \, \mu\text{m}$) to remove bacteria and other microorganisms from heat-sensitive solutions, such as certain vaccines and protein solutions.
• Product isolation: Separating solid drug crystals from the liquid mother liquor after a crystallization step.
• Air and gas purification: Filtering air in cleanrooms and sterile environments to remove particulate contaminants.
• Recovery of active ingredients: Separating active pharmaceutical ingredients (APIs) from reaction mixtures or fermentation broths.

b) The mechanisms of Filtration are:

• Surface filtration: Particles larger than the filter pores are retained on the surface of the filter medium, forming a filter cake.
• Depth filtration: Particles are captured within the internal structure of a thick, porous filter medium through mechanisms like adsorption, impaction, and entrapment.
• Cake filtration: An initial layer of solids (filter cake) forms on the filter medium, and this cake then becomes the primary filtering layer, trapping subsequent particles.
• Membrane filtration: This involves using thin, porous membranes with precisely controlled pore sizes to separate particles based on size exclusion, often used for fine particle removal and sterilization.

a) The principle of Centrifugation is the use of centrifugal force to separate components of a mixture based on differences in their density, size, and shape. When a mixture is rotated at high speed, the centrifugal force causes denser or larger particles to move away from the axis of rotation and settle at the bottom of the container, while lighter or smaller particles remain closer to the center.

b) Four (4) Pharmaceutical applications of centrifugation are:

• Separation of blood components: Used to separate plasma, serum, red blood cells, and other cellular components for diagnostic testing or therapeutic use.
• Harvesting of microbial cells: Isolating bacteria, yeast, or other cells from fermentation broths in the production of vaccines, antibiotics, or biopharmaceuticals.
• Clarification of biological fluids: Removing cellular debris, precipitates, or other particulate matter from vaccines, serums, or cell culture media.
• Separation of emulsions and suspensions: Breaking down stable emulsions (e.g., in cream manufacturing) or separating solid particles from suspensions that settle slowly under gravity.