ABSTRACT
Electrochemical methods usually involve measurement of the voltage or potential generated at electrodes immersed in an aqueous sample. The pH meter uses a glass electrode to determine the activity of hydrogen ion in a solution. The potential of the glass electrode is measured against a reference electrode, which is designed to keep a constant potential. The electrode measures only free hydrated ions, as opposed to that portion of the element tied up in complexes or present as organometallic species. Voltammetry depends upon the oxidation or reduction of a chemical species at a very small electrode. The electrodes measure the activity of the analyte, which depends on the total ionic strength of the solution. Ionic strength adjustment buffers are often added to both the samples and the standards to "swamp out" differences in ionic strength between the solutions, and give more accurate potential readings. Gas sensing electrodes are used to measure gases dissolved in aqueous solutions.
