Unit 3: Monophasic & Biphasic Liquids

February 13, 2026

Semester 1
BP103T

Introduction to Monophasic & Biphasic Liquids

Unit 3 is the heart of liquid dosage forms. You will learn about Monophasic liquids (solutions) like Gargles, Syrups, and Elixirs. The major focus is on Biphasic liquids—Suspensions and Emulsions. These are thermodynamically unstable systems, and you will learn the art of stabilizing them using suspending and emulsifying agents to prevent caking and cracking.

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Syllabus & Topics

  • 1Monophasic Liquids: Definitions & Preparations of Gargles, Mouthwashes, Throat Paints, Eardrops, Nasal drops, Enemas, Syrups, Elixirs, Liniments, Lotions
  • 2Biphasic Liquids: Suspensions – Definition, Advantages, Disadvantages
  • 3Flocculated and Deflocculated Suspensions: Differences
  • 4Stability Problems in Suspensions & Methods to Overcome (Structured Vehicle)
  • 5Emulsions: Definition, Classification, Emulsifying Agents (HLB)
  • 6Tests for Identification of Emulsion Type (Dilution, Dye, Conductivity)
  • 7Methods of Preparation – Dry Gum & Wet Gum Method
  • 8Stability Problems in Emulsions (Creaming, Cracking, Phase Inversion)

Learning Objectives

Differentiate between Elixirs and Syrups.
Compare Flocculated vs. Deflocculated Suspensions.
Explain the stability problems of Emulsions (Creaming vs Cracking).
Describe the Dry Gum and Wet Gum methods for preparing emulsions.
Perform identification tests for Emulsion type (O/W or W/O).

Frequently Asked Questions (FAQs)

Q1. What is the difference between Gargles and Mouthwashes?

Gargles are aqueous solutions used for treating throat infections and are not swallowed. Mouthwashes are used for oral hygiene (cleaning teeth and gums) and for bad breath; they are also not swallowed.

Q2. What is Flocculated Suspension?

In a flocculated suspension, particles form loose aggregates (flocs) that settle rapidly but are easily redispersed on shaking. The sediment is loose and does not form a hard cake.

Q3. Why do Emulsions crack?

Cracking (breaking) is the irreversible separation of an emulsion into oil and water layers. It occurs due to improper emulsifier selection, temperature changes, or microbial growth.

Q4. What is HLB Scale?

The Hydrophilic–Lipophilic Balance (HLB) scale ranges from 0 to 20 and classifies surfactants based on their affinity for water or oil.

  • Low HLB (3–6) → forms W/O emulsions

  • High HLB (8–18) → forms O/W emulsions

Q5. What are Throat Paints?

Throat paints are viscous liquid preparations used for localized action in the throat (pharynx). They are viscous due to a glycerin base, which helps the preparation adhere to the mucous membrane for prolonged contact.