Iodide is found in natural waters at concentrations ranging from 40 μg I−/L in coastal surface seawater to <1 μg I−/L in deep ocean water and freshwater. Higher concentrations may be found in brines, certain industrial wastes, and waters treated with iodine. Iodide is thermodynamically unstable relative to iodate in oxygenated waters.
Hanna Instruments offers a variety of technologies to measure Iodide. Potentiometric measurements with portable and benchtop pH/ISE meters are available to use with the iodide ISE for direct ion concentration measurements. Potentiometric titrations systems are available that can be used for direct measurement or for titration.
Below are the most common products used for iodide measurement.
Titrators are available to perform a titration using the iodide ISE. With this titration an iodide electrode is used as an indicator to follow the progress and detect the endpoint of a titration of iodide containing samples with silver nitrate. The electrode can be used in colored samples of high or variable ionic strength for increased accuracy of the determination. During the titration the sensor follows the decrease in iodide concentration while small additions of silver nitrate titrant are added. The silver reacts with the iodide ions forming a precipitate of silver iodide. At the stoichiometric end point, a large change in mV occurs. Hanna Instruments offers titration systems with one or two analog board inputs and options for one or two dosing pumps.
Benchtop pH/ISE meters
Benchtop pH/ISE meters include a two channel option in which a pH probe can be connected to one channel and the iodide ISE to the other. The benchtop meters have the ion charge and formula weight pre-programmed for use with the iodide ISE. The benchtop meters also have incremental methods pre-programmed including the known addition, known subtraction, analyte addition and analyte subtraction methods.
Portable pH/ISE Meters
Portable pH/ISE allow the flexibility to perform an ISE measurement with a portable even though the ISE measurement method is more suitable to a benchtop environment due to the addition of the ISA to raise the pH and the use of a magnetic stirrer to keep the sample homogenous. The portable pH/ISE meter has the ion charge and formula weight pre-programmed for concentration measurements.
Iodide Ion-Selective Electrode
Iodide electrodes are potentiometric devices used for the rapid determination of free Iodide ions in food products, plants, and as a detector for titration of iodide with silver nitrate. The electrode functions as a sensor or ionic conductor. The silver iodide pellet is practically insoluble in the test solutions being measured and produces a potential change due to changes in the sample’s ion activity. When the ionic strength of the sample is fixed by the addition of ISA, the voltage is proportional to the concentration of Iodide ions in solution; the electrode follows the Nernst equation.
The iodide ISE is available as a combination version with both indicating half cell and reference half cell or available as an indicating half cell that is used with a separate reference half cell.
Solutions for iodide measurement include ISE standards and ISA for calibration and measurement.
Accessories include polishing strips for the iodide ISE and magnetic stirrers to ensure adequate mixing when using the ISE.