Buffers in Pharmaceutical Chemistry

Definition

A buffer is a solution that resists changes in pH when small amounts of acid or base are added.

- Buffers neutralise added components, keeping the pH relatively stable.

- They are essential for processes and reactions that require **specific and stable pH ranges**.

Buffer Systems

A buffer system can be prepared using:

- Weak acid + its salt → Example: Acetic acid (CH₃COOH) + Sodium acetate (CH₃COONa)

- Weak base + its salt → Example: Ammonia (NH₃) + Ammonium chloride (NH₄Cl)

Types of Buffers

Based on chemical nature:

- Acidic Buffers: Weak acid + its salt (e.g., Acetic acid + Sodium acetate)

- Basic Buffers: Weak base + its salt (e.g., Ammonium hydroxide + Ammonium chloride)

- Neutral Buffers: Single substance acting as buffer (e.g., Ammonium acetate)

Based on use:

- Analytical Buffers

- Pharmaceutical Buffers

Buffer Capacity

Defined as the moles of strong acid or strong base required to change the pH of 1 litre of solution by one unit.

Properties of Buffers

1. pH of buffer solution remains constant.

2. pH does not change upon dilution.

3. pH remains stable even after the addition of small amounts of acid or base.

Factors for Buffer Selection

Chemical Factors:

- Should not react with other chemicals in the preparation.

- Must have reasonable chemical stability.

- Buffer capacity depends on the absolute concentration of buffer components.

Pharmaceutical Factors:

- Toxicity: Some buffers have limited use due to toxicity.

- Effect on drug action: Buffer should not interfere with the activity of medicinal ingredients.

- Microbial contamination: Buffers at neutral pH may support microbial growth, serving as nutrient media for moulds.

Role of Buffers in Pharmaceuticals

1. Maintain stable pH for medicinally active compounds.

2. Control the solubility of compounds by providing a suitable pH.

3. Influence the colour of compounds (pH‑dependent).

4. Provide stability to pharmaceutical preparations.

5. Enhance patient comfort.

6. Stabilise penicillin preparations with carbonates.

7. Stabilise milk of magnesia using citric acid.