The three elements that are most needed by plants are nitrogen (N), phosphorous (P), and potassium (K). Even though potassium is not a constituent of important compounds, it plays a remarkable role in many physiological activities in plants like the control of cellular turgor and the accumulation of carbohydrates. It increases the size of fruits, their flavor, as well as yielding a positive effect on the color and fragrance of flowers. Because of its influence on plant growth, potassium plays an important part in determining the pH of wines. Potassium also makes plants more resistant to disease.
Hanna Instruments offers a wide variety of instrumentation for measuring potassium. Products include benchtop and portable pH/ISE meters that can use a liquid membrane potassium Ion-Selective Electrode (ISE) for direct measurement. Both benchtop and portable meters have the ion charge and molecular weight pre-programmed in order to take ion concentration measurements along with multiple units of measure. The benchtop meters have incremental methods built-in.
Hanna offers a variety of chemical based methods to measure potassium. Available technologies include Spectrophotometer, benchtop and portable photometers, Checker HC, and chemical test kits. A marine version of the Checker HC allows for the measurement of potassium in seawater for the maintenance of a saltwater aquarium.
Below are the most common products used for potassium measurement.
Benchtop pH/ISE meters
Benchtop pH/ISE meters include two channel options, in which a pH probe can be connected to one channel and the potassium ISE to the other. The benchtop meters have the ion charge and molecular weight pre-programmed for use with the potassium 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 allows the flexibility to perform an ISE measurement in spaces where there is limited bench space and can be stored in a carrying case when not in use. The meter can accept other ISEs and has the ion charge and weight pre-programmed for the specific parameter.
The potassium ISE is a liquid membrane sensing electrode made with an ionophore impregnated into PVC. The electrode functions as a sensor or ionic conductor 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 potassium ions in solution and the electrode follows the Nernst equation.
The Potassium ISE is available as a combination version with both indicating half-cell and reference half-cell. It is also available as an indicating half-cell to be used with a separate reference half-cell. The reference half-cell with the skirted cone geometry is the preferred version to use.
Solutions for potassium measurement include an ISE standard and ISA for calibration and measurement.
Other solutions include the CAL Check standards for verifying and, if needed, the calibration of our portable photometers. Each CAL Check standard is supplied with a Certificate of Analysis stating the accuracy and traceability of the standard.
Spectrophotometers are available that have potassium methods in several ranges 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 to be used as well.
Benchtop photometers include multiparameter versions for nutrient analysis, water and wastewater treatment. Each photometer is customized to have the parameters used by a specific industry. All benchtops have a digital pH electrode input allowing it to be used as a traditional pH meter.
A portable photometer with two ranges is available. The Hanna 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.
Chemical Test Kits
Multiparameter Chemical Test Kits (CTK) are available to measure potassium in soil. These kits include other key parameters including nitrogen and phosphorus.
For educational use there is the Hanna Backpack Lab for Soil Quality. The Backpack Lab includes a potassium test kit along with a teacher’s guide that discusses the importance of the parameter.
Replacement reagents for the photometers and chemical test kits. The photometer reagents are available in 100 or 300 tests versions.
Accessories include the replacement potassium module for the combination ISE and magnetic stirrers for mixing. Also available are spare cuvettes and caps for the photometers.