Non - Aqueous Titrations

Chapter 6

In the above discussed chapters, it is well known that water is the major component that involves in the volumetric titrations. When an acid or base is to be used, they have to be dissolved in water to achieve the desired concentration. Moreover, water is used commonly as a solvent because of its properties such as common availability, low cost, solubilizing capability etc. However, the pharmaceutical compounds or drugs which are used in various formulations are very weak acidic or basic substances.

The solvents used in non - aqueous titrations play an important role. Generally, the solvent should be non - toxic for its wide use in analysis; it should be liquid at the time of analysis. These organic solvents are used dependent on their properties such as capability of self-dissociation, dielectric constant and acid - base character of solvent.

The non - aqueous solvents can be classified based on its proton donor - acceptor properties. The solvent exerts an influence on the acid - base properties of the solute. They are of four types: protogenicprotophilic , aprotic and amphiprotic solvents.

Substances which have both acidic and basic functional groups like amino acids, sulphonamides etc. can be titrated as acid or base under appropriate conditions of titrations. Both weak bases and weak acids can be titrated by non - aqueous titration method.

For determination of basic substances, a solution of perchloric acid in glacial acetic acid is most commonly used as Titrant. A 0.1 N perchloric acid in acetic acid is official in Indian Pharmacopoeia.

For the determination of acidic substances titrants commonly used are alkali methoxides, or tetrabutyl ammonium hydroxide. Lithium methoxide is preferred because less quantity of lithium metal is required to prepare solution and it does not allow gelatinous precipitate during titration. Solution is easy to prepare.

Estimation of Sodium Benzoate

Estimation of Ephedrine Hydrochloride

Enzymes and Protein Drugs