Lead is used in a wide variety of industries and products; including batteries, ammunition, solder, piping, pigments, insecticides, and alloys. Lead was also used in gasoline for many years as an anti-knock agent in the form of tetraethyl lead. However, lead is nonessential for plants and animals, and is toxic by ingestion, acting as a cumulative poison. For these reasons the FDA regulates lead content in food and in house paints, and the USEPA regulates lead levels in drinking water.
Hanna Instruments offers a variety of technologies to measure lead. Potentiometric measurements with portable and benchtop pH/ISE meters are available to use with the lead ISE for direct ion concentration measurements. Potentiometric titrations systems are available for either direct measurement using the ISE mode or for titration.
Below are the most common products used for lead measurement.
Titrators are available to perform a titration using the lead ISE. With this titration a lead electrode can be used as an indicator to follow the progress and detect the endpoint of a chelometric titration of lead with disodium EDTA. During the titration the sensor follows the decreasing lead concentration as small additions of disodium EDTA titrant are added. The EDTA reacts with the lead forming a complex. At the stoichiometric end point, a large change in mV occurs. Titration systems are available 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 lead ISE to the other. The benchtop meters have the ion charge and formula weight pre-programmed for use with the lead 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. The ISE measurement method requires the addition of an ISA 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.
Lead Ion-Selective Electrode
Lead electrodes are potentiometric devices used for the rapid determination of free lead ions in plating baths and as a detector for the titration of sulfate or thorium with lead perchlorate. Lead sensors are “electrodes of the third kind” because they detect cations which also form low-solubility salts with sulfide anions and forms low-solubility salts with silver.
The lead ISE is a mixed lead sulfide/silver sulfide membrane produces a potential change due to changes in the sample’s lead ion activity. When the ionic strength of the sample is fixed by the addition of ISA, the voltage is proportional to the concentration of lead ions in solution and the electrode follows the Nernst equation. The lead ISE is available as a combination electrode with both indicating half cell and reference half cell or available as an indicating half cell that will be used with a separate reference half cell.
Solutions for lead measurement include ISE standards and ISA for calibration and measurement.
Accessories include polishing strips for the lead ISE and magnetic stirrers to ensure adequate mixing when using the ISE.