Magnesium is one of the main ionic species in water which causes hardness. Magnesium is also an indispensable mineral that helps in the production of chlorophyll, the light-absorbing green pigment that serves as an energy source for plants. It also increases vitamin concentrations and aids in uptake of phosphorus within the plant body.
Magnesium 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 magnesium in the sample. Photometric analysis products include handheld colorimeters, portable and benchtop photometers, and spectrophotometers.
Titration methods are also available using a calcium ISE or photometric probe.
Below are the most common products used for measuring magnesium.
Titration systems with precision dosing pumps are available to measure magnesium. These systems can use either the calcium ISE or a photometric probe to determine the endpoint and results can be displayed in a variety of formats based on the specific need.
Photometeric Probes and Ion-Selective Electrodes
Potentiometric titration systems can use a calcium ISE or a photometric probe for the titration of magnesium. The use of a titration system allows for a precision measurement that can be automated for multiple measurements.
A photometric probe is a sensor that generates a steep millivolt potential when a solution with an indicator changes color after adding a titrant. Magnesium can be determined with EDTA and Eriochrome Black T indicator, which changes from blue to pink when magnesium binds to it. In this complexometric reaction an excess of EDTA is added then a back titration with magnesium chloride is performed with the end point being the excess magnesium reaction with the indicator to change color. The photometric probe has a wavelength of 625 nm in which there is high transmittance when the solution is pink but has a low transmittance when the solution turns blue.
The calcium ISE is a liquid membrane sensor in which an ionophore is embedded in a matrix that reacts with calcium in a lock and key fashion. An EDTA solution is used as a titrant to determine calcium concentration and calcium and magnesium in a sample. The difference between the two represents the magnesium that is present. The calcium ISE is available as either a single half-cell or combination design that is complete with a reference cell.
Spectrophotometers are available with a magenesium method 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 nutrient analysis. 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 magnesium. Multiparameter portables are available that measure calcium and magnesium hardness. The portable photometers have a CAL Check feature 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 the 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 magnesium measurement include the CAL Check standards for verification 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.