Electrochemical methods of analysis are essential tools in pharmaceutical analysis, as they offer high sensitivity, selectivity, and rapid response times.
These methods are based on the measurement of electrical signals, such as current, potential, or charge, generated by the redox (reduction-oxidation) reactions of analytes or their reactions with electroactive species.
Some of the most common electrochemical techniques used in pharmaceutical analysis include:
1. Potentiometry:
This technique measures the potential difference between a working electrode (indicator electrode) and a reference electrode, which is usually held at a constant potential.
Potentiometric measurements are useful for determining the concentration of ions or molecules in a solution.
Ion-selective electrodes (ISEs), such as the glass electrode for pH measurements, are widely used in pharmaceutical analysis.
2. Voltammetry:
Voltametric techniques involve applying a controlled potential to an electrode and measuring the resulting current.
The current is proportional to the concentration of the electroactive species in the solution.
Common voltametric techniques include cyclic voltammetry (CV), differential pulse voltammetry (DPV), and square-wave voltammetry (SWV).
These techniques can be employed for the determination of active pharmaceutical ingredients (APIs), impurities, and degradation products in drug formulations.
3. Amperometry:
Amperometry measures the current produced at a fixed potential as a result of redox reactions occurring at the electrode surface.
This technique is particularly useful for the analysis of compounds that can undergo redox reactions, such as antioxidants, vitamins, and some drug substances.
Amperometry sensors, such as glucose sensors, are widely used in pharmaceutical and biomedical applications.
4. Electrochemical impedance spectroscopy (EIS):
EIS measures the impedance of an electrochemical system over a range of frequencies.
It provides information about the kinetics of electrochemical reactions, adsorption processes, and mass transport phenomena.
EIS can be used to study the stability of pharmaceutical formulations, investigate drug release mechanisms, and evaluate the quality of solid dosage forms.
5. Conductometry:
Conductometry measures the electrical conductivity of a solution, which depends on the concentration and mobility of ions.
This technique is commonly used for the determination of the total ionic content in a sample, such as the concentration of electrolytes in intravenous solutions or the salt content in pharmaceutical formulations.
