Pharmaceutical Analysis: Principles and Titration Methods

Posted on Jul 7, 2026 in Chemistry

Limit Test for Sulphate

The Limit Test for Sulphate is used to detect and control the amount of Sulphate Impurity present in pharmaceutical substances. It is based on the formation of Barium Sulphate, which produces Turbidity/Opalescence. The turbidity of the Test Solution is compared with that of the Standard Solution.

Principle

Sulphate Ions react with Barium Chloride to form Barium Sulphate, a white insoluble precipitate.

Reaction: SO₄²⁻ + BaCl₂ → BaSO₄ ↓ + 2Cl⁻

The Turbidity produced in the test solution should Not Be Greater than that produced in the standard solution.

Method as per IP 1985

Add Dilute Hydrochloric Acid to make the solution acidic.
Add Barium Chloride Reagent to both the Test Solution and the Standard Solution.
Allow the solutions to stand for 5 Minutes.
Compare the Turbidity of the test solution with the standard solution.

Method as per IP 1996

A Modified Method is used.
Barium Sulphate Reagent is used instead of Barium Chloride Reagent.
The reagent contains Barium Chloride, Sulphate-Free Alcohol, and a small amount of Potassium Sulphate.
Alcohol prevents Supersaturation and Potassium Sulphate increases the Sensitivity of the test, producing uniform turbidity.

Indian Pharmacopoeia (IP)

The Indian Pharmacopoeia (IP) is the Official Book of Drug Standards in India. It is published by the Indian Pharmacopoeia Commission (IPC) under the Ministry of Health and Family Welfare, Government of India. It provides Standards for the quality, purity, strength, and identity of drugs.

Salient Features

Official standard book for drugs and pharmaceutical substances in India.
Contains Monographs of drugs, dosage forms, and pharmaceutical preparations.
Specifies Standards of Identity, Purity, and Strength.
Describes Tests and Analytical Methods for quality control.
Includes information on Storage Conditions and Labelling Requirements.
Provides details of Reagents, Reference Standards, and Standard Solutions.
Contains General Notices, General Chapters, and Appendices.
Regularly revised and updated.

Polarography and DME

Polarography is an Electroanalytical Method in which the Current flowing through a solution is measured as a function of the Applied Voltage. It uses a Dropping Mercury Electrode (DME) as the Working Electrode for the quantitative analysis of substances.

Principle

Polarography is based on the principle that when a Gradually Increasing Voltage is applied between the DME and a Reference Electrode, the analyte undergoes Oxidation or Reduction. The resulting Diffusion Current is directly proportional to the Concentration of the Analyte. The current-voltage curve obtained is called a Polarogram.

Conductometry

Conductometry is an Analytical Technique used to measure the Electrical Conductivity of a solution.

Advantages

Simple and easy to perform.
Provides accurate and reliable results.
No Indicator is required.
Suitable for Coloured and Turbid Solutions.
Can be used for Weak Acid–Weak Base Titrations.

Limitations

Conductivity is affected by Temperature.
Electrodes require Proper Cleaning and Maintenance.
Not suitable for solutions with Very Low Conductivity.
Presence of Impurities may affect results.

Potentiometry

Potentiometry is an Electroanalytical Technique used to measure the Potential Difference between a Reference Electrode and an Indicator Electrode without drawing significant current.

Applications

pH determination using a glass electrode.
Acid–Base, Redox, Precipitation, and Complexometric titrations.
Determination of Metal Ions in pharmaceutical samples.

Glass Electrode

A Glass Electrode is an ion-selective electrode used to measure the pH (hydrogen ion concentration) of a solution. It works on the principle of membrane potential developed due to the difference in H⁺ ion concentration across a thin glass membrane.

Cerimetry

Cerimetry is a type of redox titration where Cerium(IV) Sulfate (Ce⁴⁺) is used as a strong oxidizing agent for the estimation of reducing agents in an acidic medium.

Permanganometry

Permanganometry is a Redox Titration method in which Potassium Permanganate (KMnO₄) is used as the Oxidizing Agent. It acts as a Self Indicator, and the appearance of a Permanent Light Pink Colour indicates the end point.

EDTA: Structure and Properties

EDTA (Ethylenediaminetetraacetic Acid) is a Hexadentate Chelating Agent that forms stable Complexes with metal ions. It is widely used in Complexometric Titrations for the estimation of metal ions like Calcium and Magnesium.

Fajan’s Method

Fajan’s Method is a Precipitation Titration method in which Adsorption Indicators (e.g., Fluorescein, Eosin) are used to detect the End Point. It is mainly used for the estimation of Chloride, Bromide, and Iodide ions.

Primary and Secondary Standards

Primary Standard: A Highly Pure, Stable, and Non-Hygroscopic substance used to prepare a standard solution directly (e.g., Sodium Carbonate, Oxalic Acid).
Secondary Standard: A solution whose concentration is determined by Standardization against a primary standard (e.g., HCl, NaOH, KMnO₄).

Significant Figures

Significant figures are the Meaningful Digits in a measurement that indicate the Accuracy and Precision of the result. They include all Certain Digits and the First Uncertain Digit.

Accuracy vs. Precision

Accuracy: The degree of closeness between the Measured Value and the True Value (Correctness).
Precision: The degree of closeness between Repeated Measurements of the same sample (Reproducibility).

Reference Electrodes

Standard Hydrogen Electrode (SHE): Primary reference electrode with a potential of 0.00 V.
Saturated Calomel Electrode (SCE): Secondary reference electrode using Mercury and Mercurous Chloride.
Silver–Silver Chloride Electrode (Ag/AgCl): Stable electrode using a Silver wire coated with Silver Chloride.

Iodimetry vs. Iodometry

Iodimetry: Direct titration using Standard Iodine Solution to estimate reducing agents.
Iodometry: Indirect titration using Standard Sodium Thiosulphate to estimate oxidizing agents by liberating iodine from Potassium Iodide.

Diazotization Titration

A Volumetric Analysis method used for the estimation of Primary Aromatic Amines. The amine reacts with Sodium Nitrite in the presence of Hydrochloric Acid at 0–5°C to form a Diazonium Salt.

Gravimetric Analysis

A Quantitative Analytical Method where the analyte is converted into a Pure, Stable, and Insoluble Compound. The precipitate is filtered, washed, dried/ignited, and weighed to calculate the analyte concentration.

Masking and Demasking

Masking Reagents: Chemicals that react with Interfering Metal Ions to form a stable complex, preventing interference.
Demasking Reagents: Chemicals that break the masked complex to release the metal ion for analysis.

Non-Aqueous Titration

Titration carried out in a Solvent Other Than Water, used for the analysis of Weak Acids and Weak Bases. Solvents are classified as Protogenic, Protophilic, Amphiprotic, or Aprotic.

Acid–Base Indicators

Weak Organic Acids or Bases that change colour according to the pH of the solution. Theories include the Ostwald Theory (Ionization) and the Quinonoid Theory (Structural change).