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Non-aqueous titration is the titration of weakly acidic or basic analytes in a solvent medium that lacks water. The solute is dissolved in a non-aqueous solvent, and is further titrated with an acid or base titrant.
The principle of acid-base titration and non-aqueous titration is the same. It states that an acid donates a proton to another chemical and a base accepts a proton.
The interference of water molecules in titration is the rationale for non-aqueous titrations. Water is a weak acid and a weak base. Water molecules compete with various bases and acids dissolved in them for proton donation and acceptance. Water competition makes it harder to determine the titration’s endpoint. As a result, a titration process that does not include the interference of water molecules is required; hence, non-aqueous solvents are utilised to assess chemicals, a process known as non-aqueous titration.
Types of Solvents Used in Non-Aqueous Titrations
There are 4 types of solvents used in non-aqueous titration.
1. Aprotic Solvents:
A hydrogen atom is bound to oxygen, fluorine, or nitrogen in this form of non-aqueous solvent. These are chemically inert and have a neutral charge. Two examples are chloroform and benzene.
2. Protogenic Solvents:
These are acidic solvents that quickly donate protons. They are usually used to boost the alkalinity of weak acids and strengthen weak bases. Two examples are acetic and sulphuric acid.
3. Protophilic Solvents:
These are basic solvents with a high proton acceptance tendency. They create solvated protons when they react with acids. Examples are amines, liquid and ammonia.
4. Amphiprotic Solvents:
These are solvents with acidic and basic qualities, as well as protogenic and protophilic solvent properties. Alcohols and acetic acid are two examples.
Indicators Used for Non-Aqueous Titrations
The following indicators used in non-aqueous titrations:
The resonant, ionised and unionised forms of indicators are used for non-aqueous titration; however, the colour change at the endpoint of reaction varies among titrations depending on the titrant nature.
- Crystal violet indicator: It is widely used and employed in glacial acetic acid titration as a 0.5% w/v solution.
- Methyl red indicator: It is made in a 0.2% w/v dioxin solution and its endpoint indicates a change in colour from yellow to red.
- Naphtholbenzein indicator: The naphtholbenzein indicator is made in a 0.2% w/v solution as ethanoic acid and indicates a colour change from yellow to green at the endpoint.
- Quinaldine red: Most drug assays use it, and its colour shifts from purplish red to light green at the endpoint.
- Thymol Blue: It is frequently used as a pH indicator in various titrations. It is utilised as a 0.2% w/v solution in methanol, with a yellow to blue colour change.
Advantages of Non-Aqueous Titration
- Non-aqueous titration is used to titrate organic acids or bases that are insoluble in water and soluble in non-aqueous solvents.
- It can titrate weak acids or bases that are impossible to titrate in water.
- Organic acids with a strength comparable to water can be easily titrated.
- It can also be used to titrate samples that contain acid combinations.
- This method of titration is easy to carry out and does not require any specific laboratory equipment or glassware.
- Internal indicators can deliver a quick and precise result.
- This titration is crucial in pharmacopoeial assays and for biological substances.
- The potentiometric approach can be used to automate the operation.
Disadvantages of Non-Aqueous Titrations
- Because this is an open system, temperature and moisture may impact the outcomes; hence, they must be controlled.
- The non-aqueous titration solvent is more expensive than the aqueous titration solvent.
- As this titration is non-specific, contamination may occur.
- A volatile solvent can contaminate the environment more than aqueous solvents.
- The non-aqueous solvents should be calibrated after each usage in non-aqueous titration.
Conclusion:
Titration is quantitative chemical analysis, commonly known as the volumetric or titrimetry method. It is a procedure in which a known concentration titrant is given to an unknown-concentration sample solution until the reaction is complete, usually using an indicator to identify the endpoint.
Non-aqueous titration’s principle is similar to that of acid-base titration, which states that if an acid donates a proton to another substance, a base accepts a proton. Various solvents, such as protogenic solvents, protophilic solvents, aprotic solvents, and amphiprotic solvents are used in non-aqueous titration.
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