Summary
Environmental analysis entails the monitoring of certain chemical substances in the environment to identify pollution. Some of the main groups of chemical substances include herbicides, pesticides, semi-volatile and volatile organic compounds, metals and their ions. Various techniques are available for detecting the presence and quantities of these chemicals including electrochemistry, gravimetry, spectrometry and volumetric analysis (Whitcombe, Kirsch, & Nicholls 2014). The choice of method is determined by the chemical compound to be analyzed, the time available, the level of accuracy needed and the available time. This paper looks at the electrochemical method in the analysis of common metals such as iron, cobalt, aluminum and nickel as well as their ions.
Electrochemical Methods
Electrochemical methods of analysis entail the use of various precise techniques such as potentiometry, coulometry, amperometry, and voltammetry (Taillefert & Rozan 2002). These methods take advantage of differences in parameters between two electrodes to determine the concentration of the analyte of interest. For example, in potentiometry, the potential difference between two electrochemical cells can be quantified using a high impedance voltmeter with minimal current. On the other hand, colorimetry depends on the oxidation and reduction of an analyte within a given time to ensure its quantitative transformation to a different oxidation state.
Advantages of Electrochemical Methods Compared to other Conventional Methods in the Determination of Metal Ions
Advances in electrochemical technologies have enabled the accurate determination of trace elements and ions in the environment. For example, conductimetry can determine salinity while voltammetric sensors can enable the analysis of several species simultaneously (Taillefert & Rozan 2002). In contrast, conventional methods of measuring these species such as spectrophotometry can only be used to measure one analyte at a time due to the use of specific standards and blanks for each test.
Another advantage of electrochemical methods is that they can be used to measure more than one parameter in a given sample as opposed to other techniques such as gravimetry, and spectrophotometry, which only measure one aspect (concentration or weight respectively) at a time. For instance, potentiometry can determine the pH of a solution as well as the metal ions present in the solution.
Techniques such as voltammetry are not influenced by matrix problems such as elevated salinity (Farghaly, Hameed, & Abu-Nawwas 2014). The method also has high sensitivity and selectivity, which makes it ideal for the quantification of trace elements.
Progress in nanotechnology has led to the development of nanoelectrodes, which have been incorporated in atomic force microscopy and utilized in the mapping of the chemical constituents at the solid-water boundaries.
It is also possible to incorporate these techniques into gadgets meant for laboratory experimentation and online measurements. Electrochemical techniques also use microsensors, which enable the gathering of data at the micrometer scale thus ensuring high sensitivities compared to the conventional measurement techniques such as volumetric analysis and gravimetry that have low sensitivities due to the limitation of the measuring vessels and weighing balances.
Electrochemical techniques are capable of determining the chemical speciation of trace elements in their physical environments after physical and chemical separations, which may not be possible using the other conventional techniques that require the collection of samples and analysis in a laboratory setting.
Disadvantages of Electrochemical Methods Compared to other Conventional Methods in the Determination of Metal Ions
One disadvantage of electrochemical techniques is that the interference of ions hampers the use of NO3– and NH4+ electrodes in maritime environs. Another shortcoming is that the detection thresholds of ion-selective electrodes do not allow for the detection of metals in their natural habitats.
Some techniques such as chronoamperometry, which is a form of coulometry, have limited applicability for the analysis of environmental samples (Taillefert & Rozan 2002). Conversely, conventional techniques such as volumetric analysis and spectrometry can be used in all samples provided their standards are available.
References
Farghaly, O. A., Hameed, R. A. & Abu-Nawwas, A. A. H 2014, “Analytical application using modern electrochemical techniques,” International Journal of Electrochemical Science, vol.9, pp. 3287-3318.
Taillefert, M & Rozan, T. F 2002, “Electrochemical methods for the environmental analysis of trace elements biogeochemistry,” in Taillefert, M & Rozan (eds), Environmental chemistry, American Chemical Society, USA, pp. 2-14.
Whitcombe, M. J., Kirsch, N. & Nicholls, I. 2014, “Molecular imprinting science and technology: a survey of the literature for the years 2004–2011,” Journal of Molecular Recognition, vol.27 no.6, pp. 297-401.