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Phosphates are used in a number of everyday products, such as cola drinks to enhance flavor and tartness, antifreeze as a pH buffer, and french fries to delay darkening of the cut potatoes. They are also extensively used in detergents and cleaning fluids because of their ability to soften water and remove soil deposits. Phosphate is essential for the growth and development of plant roots, stems, flowers and seeds, and is commonly added to fertilizers. However, high concentrations of phosphates in agricultural runoff can cause environmental pollution, as a primary cause of eutrophication. Local laws govern the use of phosphates and the discharge levels into streams and waterways.

The amount of phosphate can be expressed in two different ways:

  • Phosphate (PO43-) also known as orthophosphate
  • Phosphorous (P) also known as orthophosphate as phosphorus (PO4-P).

Orthophosphate is a molecule with a phosphorus atom surrounded by four oxygen atoms, and a negative three charge. Phosphate or orthophosphate, is a measure of the amount of orthophosphate (PO43-) molecules in a sample. While phosphorus or orthophosphate as phosphorus (PO4-P), is a measure of the amount of phosphorous (P) ions in a sample. This means that when measuring phosphate, the four oxygen atoms bound to the phosphorus atom are included in the measurement. However, it is possible to easily convert between the two measurements with simple multiplication or division. To convert a result from phosphorous (P) to phosphate (PO43-) you simply need to multiply by 3.06. Conversely, to convert from phosphate to phosphorus you just need to divide by 3.06. The reason this works is because the orthophosphate molecule (PO43-) is approximately 3.06 times heavier than the phosphorus atom.

Hanna offers a variety of chemical based methods to measure phosphate. Available technologies include Spectrophotometer, benchtop and portable photometers, Checker HC and Chemical Test Kits.

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Portable Photometers

Portable photometers are available in two ranges. The portables are able to display phosphate results in multiple chemical forms. The portable photometers have a CAL Check feature that allows for performance verification, and if needed, recalibration using the CAL Check standards. The meters are available as a meter only option or as a kit. The kit version include a rugged carrying case and CAL Check standards

Benchtop Photometers

Benchtop photometers include multiparameter versions for water treatment, wastewater treatment, environmental, and aquaculture. Each photometer is customized with the parameters used by a specific industry. The benchtop photometers are able to display phosphate results in multiple chemical forms. All benchtop have a digital pH electrode input allowing it to be used as a traditional pH meter.


Spectrophotometers are available that have phosphate 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.


Solutions for phosphate measurement 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.

Chemical Test Kits

Phosphate Chemical Test Kits (CTK) are available for basic water quality testing. There are two options for a phosphate CTK. One is for basic color cube with 5 points of resolution while the other option is for the Checker Disc that has 50.

Multiparameter CTKs are available for boiler and cooling tower water treatment. Both kits include other key parameters.

For educational use there are the Hanna Backpack Labs. Both of the Water Quality and Marine Science Backpack Labs that include a phosphate test kit along with a teacher’s guide that discusses the importance of the parameter.

Checker HC

Checker HC, like a chemical test kit, are a reagent based design 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. The change in color is not subjective as with using the naked eye. A marine version is available with chemistry that is compatible for use with saltwater aquariums.