Manganese is associated with iron minerals, and occurs in nodules in ocean, fresh waters, and soils. It is an essential trace element for plants and animals. Manganese is used in steel alloys, batteries, and food additives. The common aqueous species are the reduced Mn2+ and the oxidized Mn4+. The chemistry of manganese in water is similar to that of iron.
Soluble manganese in groundwater is usually in the reduced state (Mn2+). Upon exposure to air or other oxidants, groundwater containing manganese usually will precipitate black MnO2. Elevated manganese levels therefore can cause stains in plumbing/laundry, and cooking utensils.
The United Nations Food and Agriculture Organization recommends that the maximum level for manganese in irrigation waters is 0.2 mg/L. The U.S. EPA secondary drinking water standard MCL is 50 μg/L.
Manganese can be measured photometrically with reagents. Photometric analysis is based on the Beer-Lambert principle of absorbance in which the intensity of the color produced is proportional to the concentration of manganese in the sample. Photometric analysis products include handheld colorimeters, portable and benchtop photometers, and spectrophotometers. The low-range method uses an adaptation of the PAN method. The high-range method uses an adaptation of Standard Methods for the Examination of Water and Wastewater, Periodate Method.
Below are the most common products used for measuring manganese.
Spectrophotometers are available that have manganese methods pre-programmed into the meter. The spectrophotometer offers the highest precision due to the quality of the optical system that has a wavelength accuracy of +/- 1.5 nm. The spectrophotometer allows for custom methods.
Benchtop photometers include multiparameter versions for water quality, wastewater and water conditioning. Each photometer is customized to have the parameters used by a specific industry. All benchtop have a digital pH electrode input allowing it to be used as a traditional pH meter.
Single parameter photometers are available to measure manganese. Multiparameter portables are available that measure calcium and manganese hardness. The portable photometers have a CAL Check feature that allows for performance verification and, if needed, recalibration using the CAL Check standards. The portable meters are available as a meter only or as a kit. The kit version includes a rugged carrying case and CAL Check standards.
Checker HC, like chemical test kits, are reagent based with a color change based on concentration. The handheld colorimeters, like portable and benchtop instrumentation, use the Beer-Lambert principle to determine the color change.
Reagents include the reagents used with Checker HC and photometers.
Solutions for manganese measurement include the CAL Check standards for verifying and, if needed, the calibration of portable photometers. Each CAL Check standard is supplied with a Certificate of Analysis stating the accuracy and traceability of the standard.
Accessories include cuvette cleaning solution, microfiber cloths, and replacement cuvettes and caps for photometers.