1. Direct titration:
In this method, metal ions in the sample are titrated directly with a chelating agent, such as EDTA.
The endpoint is detected using an indicator like Eriochrome Black T or by instrumental methods (e.g., potentiometric or conductometric detection).
Direct titrations are the most straightforward and commonly used complexometric titrations.
2. Back titration:
Back titration is used when the direct titration of the metal ions is difficult, for instance, when the endpoint is not well-defined, or the reaction is too slow.
In this method, the metal ions are first reacted with an excess of chelating agent.
The unreacted chelating agent is then titrated with a standard solution of a metal ion, such as zinc or magnesium, whose concentration is accurately known.
The endpoint is detected using the same methods as in direct titration.
3. Replacement (displacement) titration:
Used when the metal ions do not readily form a stable complex with the chelating agent or when the endpoint is difficult to detect.
A metal ion (such as calcium or magnesium) that readily forms a stable complex with the chelating agent is added to displace the analyte metal ions.
The displaced metal ions are then titrated with the chelating agent, and the endpoint is detected similarly to direct titration.
4. Alkalimetric titration:
Although not a type of complexometric titration, alkalimetric titration refers to titrations used to determine the acidity or alkalinity of a solution using a strong acid or base.
Also known as acid-base titrations, these are not typically categorized under complexometric titrations.
This arrangement clarifies the different types of complexometric titrations, highlighting the appropriate classification and method of detection for each.