Acid-Base Titration

Acid base titration can be defined as a titration reaction which takes place between an acid and base in which we determine the concentration of an acid or base by completely neutralising it with an acid or a base with a known concentration. These reactions help us determine the concentration of an acid or a base in terms of normality, molarity, molality, etc. In the process, we also make use of the PH indicator (phenolphthalein) to monitor the process of the reaction by knowing the colour of the pH indicator. The pH indicator phenolphthalein has a pH range between 8 to 10, which makes it an overall good indicator for the process of titration.

Titration

Titration requires solid or weak acid or a base for knowing the concentration or determining whether the given solution is a strong or weak acid or base. The experiment involves a titrant and an acid or a base.

There can be different types of titrations like:

1) strong acid strong base

2) strong acid weak base

3) weak acid weak base

4) weak acid strong base

There is an equivalence point at which the acid and base neutralise exactly, i.e. there are equal numbers of moles of hydrogen and hydroxides. Now accordingly, the experimentalist can draw the titration curve. There is a use of an indicator through which we can detect the change and tell whether the solution has been neutralised or not. The common indicators used are phenolphthalein and methyl orange, and sometimes even malachite green can also be used. But for pharmaceutical industries, electrodes of pH metres are immersed as an indicator.

Experiment

1) Place an unknown concentration of an acid or a base in a beaker and add an indicator or electrode of a pH metre.

2) Fill the buret with a titrating solution of known concentration, and this is called the titrant or standard solution.

3) Standard solution is added slowly by measurements in the solution in the beaker until the equivalence is attained. Now, by calculation using mathematical formulas, the concentration of the unknown solution can be obtained. 

Importance of titration in the pharmaceutical industry

There are many reasons for using acid-base titration in pharmaceuticals, for example, analysis, quality control and product development, content analysis by redox titration and purity analysis of the pharmaceutical active substances. Purity analysis is used for determining active ingredients in the products, or example, acetylsalicylic acid in aspirin or vitamin c in multivitamin tablets. It is also used for the purity control of the drug additives used for the synthesis of medicinal preparations. One example is purity control of ephedrine hydrochloride, which is used as a cough syrup for the treatment of bronchial asthma.

There are many methods of titration in pharmaceuticals:

1) Titration in non-aqueous solvents: it is for weak acids and bases 

a) Non-aq. titration of bases: for amines determination

R-NH₂ + HClO₄ → R-NH₃⁺ + ClO₄^–

Direct titration of amines: 

-Benzyl nicotinate used in rheumatism

Protonated amine salts titration:

-Diphenylpyraline Hydrochloride 3 is an antihistamine.

HClO₄ in glacial acetic acid is used in non-aqueous titration of amines.

Solvents used can be acetic acid, acetic acid anhydride, methanol and acetone.

Titrants used can be perchloric acid, perchloric acid in glacial acetic acid, and perchloric acid in acetic anhydride.

b) Non-aq. titration of acids: for aromatic acids determination

ROH + (R’)₄NOH →  RO^– + N(CH₃)₄⁺ + H₂0

Direct titration of phenol and its derivatives

-Phenol and Rutoside.

Solvents used can be 1,2-Diaminoethane, dimethylformamide, and acetone.

Titrants used can be TMAH, TBAH, and 2-propanol/methanol mixtures.

2) Titration in aqueous solution: It is an analytic process in which water is used as a solvent for the determination of the amount of desired substance.

Buffer capacity

It is a solution which is capable of keeping the pH value constant when a small amount of either acid or a base is added; its resistance to pH changes is known as buffer capacity. This type of solution can be prepared by combining a weak acid and its salt with a strong base and vice-a-versa. The buffer capacity usually depends on the amount of substance of given weak acid and its conjugate base in the buffer solution.

Conclusion

In this article, we got to know about titration and its uses in the pharmaceutical industry. There are many other types of titration, but the objective of this article was to focus on acid-base titration and its importance in the pharmaceutical industry, the uses of acid bases titration in the pharmaceutical industry and its analysis. We also discussed different types of acid-base titration like the titration in a non-aqueous and aqueous solvent and their examples concerning diseases, and lastly, about the buffer solution.