Astringent - Pharmaceutical Inorganic Chemistry B. Pharma 1st Semester



• Astringent

• The monograph analysis of:

 Zinc sulphate

 Potash alum

Learning Objectives

At the end of this lecture, the student will be able to:

• Define astringent

• Explain the monograph analysis of:

 Zinc sulphate

 Potash alum


• The word "astringent" derives from Latin adstringere, meaning "to bind fast"

• Definition: Astringent is a drug that reacts chemically with cellular proteins producing limited coagulation which is accompanied with shrinkage of body tissues

• Astringent protects from external irritation and reduces cellular permeability

• It also possesses local styptic and local antiseptic actions

 Astringent medicines cause shrinkage of mucous membranes or exposed tissues and are often used internally to check discharge of blood serum or mucous secretions

 This can happen with a sore throat, hemorrhages, diarrhea, or with peptic ulcers.  Externally applied astringents, which cause mild coagulation of skin proteins, dry, harden, and protect the skin

 Acne sufferers are often advised to use astringents if they have oily skin

Uses of astringents:

• Cleaning the face and preventing Acne Breakouts

• Stopping bleeding

• Relieving the discomfort and itching of insect bites, minor abrasions and Athlete’s foot

• Haemorrhoids

Monograph of zinc sulphate

Name: zinc sulphate

Chemical formula: ZnSO4, 7H2O

Molecular weight: 287.5

Standards: Zinc Sulphate contains not less than 99.0 per cent and not more than 104.0 per cent of ZnSO4, 7H2O

Method of Preparation:

Zn + H2SO4 + 7H2O à ZnSO4 7H2O + H2

Properties of zinc sulphate:


• A Colourless, transparent crystals or a white, crystalline powder

• Odourless

• Efflorescent

Solubility: Very soluble in water and glycerine and insoluble in alcohol

Test for purity

• Appearance of solution

• Chlorides

• Arsenic

• Iron

• Acidity/Alkalinity

Assay Principle

Complex metric, Direct titration

ZnSO4 + 2CH3COOH à Zn (CH3COOH)2

Zn (CH3COOH)2 + di Na EDTA à Zn EDTA complex

Indicator: xylenol orange triturate

Buffer: hexamine

Titrant: Di sodium EDTA

Colour change: violet pink- yellow

Storage: Store protected from moisture, in non-metallic containers

Medicinal uses:

• Astringent

• Emetic

Monograph of Potash alum

Name: Potash alum

Chemical formula: KAL(SO4)2.12H2O

Molecular weight: 474.4

Standards: It contains not less than 99.5 per cent

Method of Preparation:

K2SO4 + Al2(SO4)3 + 24H2O à KAL(SO4)2.12 H2O

Properties of Potash alum:


• A Colourless, transparent crystals or a white, crystalline powder

• Sweet astringent taste

• Heated to 200oC, loses its water of crystallisation and becomes anhydrous

Solubility: Very soluble in water and insoluble in alcohol

Test for purity

• Heavy metals

• Zinc

• Arsenic

• Iron

• Ammonium salt

Storage: Store in a well closed containers

Medicinal uses:

• Astringent and antiseptic

• Due to its protein precipitation used in the preparation of toxoids

• Astringents: protein precipitants

• Zinc sulphate: Is prepared by adding sulphuric acid on metallic zinc, assayed by complexometric direct titration and medicinally used as astringents and emetic

• Potash alum: used as astringent, double salt, used for water purification

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