Activity vs. Concentration
The photo below provides a demonstration of the difference between activity and concentration using the indicator methyl green. The indicator is yellow in its acid form (beaker a: 1.0 M HCl) and […]
Illustration
Enzyme Electrode
A gas-sensing electrode can be modified to create a potentiometric electrode that respond to a biochemically important species, such as enzymes. One example of an enzyme electrode is the urea electrode, which is […]
Gas-Sensing Membrane Electrode
A number of membrane electrodes respond to the concentration of a dissolved gas. The basic design of a gas-sensing electrode consists of a thin membrane that separates the sample from an inner […]
Liquid Membrane Ion-Selective Electrode
Another class of ion-selective electrodes uses a hydrophobic membrane containing a liquid organic complexing agent that reacts selectively with the analyte. Three types of organic complexing agents have been used: cation exchangers, […]
Solid-State Ion-Selective Electrode
Schematic diagram of a solid-state electrode, the membrane for which is either a polycrystalline inorganic salt or a single crystal of an inorganic salt. We can fashion a polycrystalline solid-state ion-selective electrode […]
pH Electrode
Schematic diagram showing a combination glass electrode for measuring pH. The indicator electrode consists of a pH-sensitive glass membrane and an internal Ag/AgCl reference electrode in a solution of 0.1 M HCl. […]
Schematic Diagram of a Membrane Electrode
Shown here is a schematic diagram of a typical potentiometric cell that includes a membrane electrode (in this case, an ion-selective membrane). The membrane separates the sample solution, which contains the analyte […]
Reference Electrodes
In a potentiometric electrochemical cell one half-cell provides a known reference potential and the potential of the other half-cell indicates the analyte’s concentration. The ideal reference electrode provides a stable, known potential so […]
Junction Potentials
A junction potential develops at the interface between two ionic solution if there difference in the concentration and mobility of the ions. Consider, for example, a porous membrane separating solutions of 0.1 […]
Schematic Diagram of a Potentiometric Electrochemical Cell
Shown here is the schematic diagram of a typical potentiometric electrochemical cell. The electrochemical cell consists of two half-cells, each consisting of an electrode immersed in a solution of ions whose activities […]
Family Tree for Interfacial Electrochemical Techniques
Shown here is a family tree that highlights a number of interfacial electrochemical techniques. The specific techniques are shown in red, the experimental conditions are shown in blue, and the analytical signals […]
Schematic Diagram of a Manual Potentiostat
A potentiostat is used to set and control the potential of a working electrode. A schematic diagram for a manual potentiostat is shown here where W is the working electrode, A is the auxiliary […]