With a wide range of techniques that enable the detection and quantification of chemical species based on their electrical properties, electroanalytical methods have a fundamental role in chemical analysis. While being relatively simpler and less expensive than other techniques, electroanalytical methods find applications in numerous fields.
By providing sensitive, accurate, and real-time data, they have become indispensable tools in modern analytical chemistry, supporting advances in fields such as environmental monitoring, pharmaceutical development, biomedical diagnostics, and industrial process control.
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Electroanalytical Methods: Foundations and Impact
Electroanalytical methods measure the flow of electrons generated by the redox reactions occurring between the analyte and the electrode surfaces by using electrodes (electrically conductive probes) in contact with the analyte solution.
The measurement of electrical parameters related to the identity and concentration of the analyte(s), such as current, potential, and charge, provides insight into chemical systems.
These highly sensitive and selective methods can detect low concentrations of analytes, often in the presence of complex matrices. Moreover, they allow real-time monitoring of chemicals, which is useful for some processes, from environmental analysis to diagnostics.
Key Electroanalytical Techniques
The main electroanalytical methods are potentiometry, voltammetry, amperometry, and coulometry, which differ for to the electric parameters measured.
Potentiometry measures the electric potential between the electrodes while maintaining a constant electric current to determine the concentration of ions in a solution. Measurements are rapid and require minimal sample preparation, although the selectivity may suffer from interferences from other ions.
In voltammetry, the current is measured as a function of an applied potential and can provide information on the kinetics and mechanism of electrochemical reactions. However, it requires careful calibration and data interpretation.
Amperometry measures the electric current while keeping a constant potential. It is used in sensors where the current is directly proportional to the analyte concentrations and offers rapid response times and high sensitivity. However, it can be susceptible to electrode fouling and interference from other electroactive species.
Coulometry is used for the quantification of substances and measures the total charge passed during the complete electrochemical conversion of an analyte. Although calibration is not needed, measurements can be time-consuming and require a thorough understanding of the electrochemical system.
Trending Technologies: A Comprehensive Guide to Spectrophotometry
Innovations in Electroanalytical Methods
Recent advancements in electroanalytical methods have focused on enhancing sensitivity, selectivity, and portability. Significant performance improvements have been achieved with the use of innovative electrode materials, such as nanomaterials and conductive polymers.
The ability to control the size, composition, and surface properties of nanomaterials enables to tailor the electrodes characteristics, with increased surface area, enhanced conductivity, and improved biocompatibility.1
The development of microfabrication and additive manufacturing techniques (e.g., 3D printing, inkjet) has led to better detection capabilities and sensor selectivity.
Microfabrication has also enabled the creation of lab-on-a-chip systems, which integrate multiple analytical functions into a single, compact device, thus facilitating the development of portable sensors.
Applications of Electroanalytical Methods
Electroanalytical methods find applications in several fields. They are largely used in environmental monitoring to detect pollutants such as heavy metals, pesticides, and organic contaminants in water and soil.
For instance, a sensor made from Fe3O4 and ZnO incorporated within carbon nanotubes-nylon nanofibers showed good performance for the detection of lindane – an organochlorine compound used as an insecticide in agriculture and a potential carcinogen – with a limit of detection (LOD) of 32 nM.
Electrodes based on graphene and carbon nanotubes have been extensively used to detect heavy metals, with some of them showing promise in the simultaneous detection of Tl+, Pb2+, and Hg2+.2
Advances in voltammetry and amperometry have enabled the development of uniquely designed electrodes for the detection of a broad range of emerging contaminants, including polyfluoroalkyl substances (PFAS).3
In biomedical diagnostics, electroanalytical sensors can be used to monitor physiological parameters.
Amperometric sensors for glucose are convenient and accurate means of blood sugar monitoring, where electrodes detect the current generated when the glucose in the blood sample mixes with the glucose enzyme reagents in the test strip. There is also increasing interest in glucose sensors that use other bodily fluids, such as sweat or saliva, which a smartphone could read.4
Analytical Chemistry and Life Sciences
Challenges and Limitations
One of the main limitations that can impair the performance of electroanalytical methods is electrode fouling, where the electrode surface becomes contaminated. This can be mitigated with regular maintenance and the development of anti-fouling coatings.
Interference from matrices is another challenge, as it can lead to false signals and inaccurate results. For instance, the complex nature of real water samples (pH, turbidity, presence of organics, and multiple metal ions) makes the determination of heavy metals extremely difficult.
Calibration and standardization also pose challenges, particularly in heterogeneous samples. Internal standards and reference materials can improve accuracy and reproducibility.
These methods require electrochemically active compounds. Therefore, there are challenges with the development of sensors for the detection of inert species such as PFAS, which would require an indirect detection mechanism.
Future Directions in Electroanalytical Methods
The development of wearable sensors for monitoring physiological parameters in real time is a rising trend. These devices can provide continuous data, offering insights into health and disease states.
Particularly, there is growing interest in smartphone-based electrochemical sensors for glucose monitoring. Wearable glucose monitoring through electrochemical detection in saliva, sweat, and tears is developing rapidly and is entering the commercialization stage.5
The use of nanomaterials as matrices, together with selective coatings and ink printing, allows the development of novel electrodes.
The integration of nanocomposite materials into microchips enables lab-on-a-chip sensing devices with high sensitivity and high throughput screening. This paves the way for a new generation of low-cost, portable, electrochemical sensors.
Conclusion
Thanks to unique features such as sensitivity, selectivity, and ease of use, electroanalytical methods are widely used across multiple fields. As technology advances, the capabilities of these methods keep expanding.
Continued innovation and research are essential to overcome existing challenges and develop better technologies, ensuring that electroanalytical methods remain key in chemical analysis.
References
- Terán-Alcocer, Á., Bravo-Plascencia, F., Cevallos-Morillo, C. & Palma-Cando, A. (2021). Electrochemical Sensors Based on Conducting Polymers for the Aqueous Detection of Biologically Relevant Molecules. Nanomaterials (Basel), doi:11.10.3390/nano11010252.
- Hou, H., Zeinu, K. M., Gao, S., Liu, B., Yang, J. & Hu, J. (2018). Recent Advances and Perspective on Design and Synthesis of Electrode Materials for Electrochemical Sensing of Heavy Metals. ENERGY & ENVIRONMENTAL MATERIALS, 1, 113-131.https://doi.org/10.1002/eem2.12011. Available: https://onlinelibrary.wiley.com/doi/abs/10.1002/eem2.12011
- Hassan, M. H., Khan, R. & Andreescu, S. (2022). Advances in electrochemical detection methods for measuring contaminants of emerging concerns. Electrochemical Science Advances, 2, e2100184.https://doi.org/10.1002/elsa.202100184. Available: https://chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/elsa.202100184
- Alhaddad, A. Y., Aly, H., Gad, H., Al-Ali, A., Sadasivuni, K. K., Cabibihan, J. J. & Malik, R. A. (2022). Sense and Learn: Recent Advances in Wearable Sensing and Machine Learning for Blood Glucose Monitoring and Trend-Detection. Front Bioeng Biotechnol, 10, 876672. doi:10.3389/fbioe.2022.876672.
- Xu, J., Yan, Z. & Liu, Q. (2022). Smartphone-Based Electrochemical Systems for Glucose Monitoring in Biofluids: A Review. Sensors (Basel), 22.doi:10.3390/s22155670.
Further Reading