Phosphate HR

Test Method Technical Information


Tests For: High Levels of Phosphate in Boiler Water
Tests Range: 0–100 mg/L
Reagent Chemistry Used: Vanadomolybdophosphoric acid
Basis of Test Method: Standard Method 4500-P-C
Method Detection Limit*: 1 mg/L
Limit of Quantification**: 3 mg/L

*The Method Detection Limit (MDL) is defined as the minimum measured concentration of a substance that can be reported with 99% confidence to be different from the method blank results.
**The Limit of Quantification (LOQ) is the smallest quantity that can be detected with reasonable certainty for a given analytical procedure.

Testing for Phosphate HR

Phosphates are extensively used for treating water in boilers and steam raising plant. Phosphates are added to control the deposition of sediment and deposits within the boiler. It is an essential part of the treatment programme to monitor the phosphate level to ensure this is within the correct range of deposition control.

The Palintest Phosphate HR test provides a simple method of measuring phosphate levels in boiler waters over the range 0–100 mg/l PO4.

Reagent Chemistry

The Palintest Phosphate HR test is based on the Vanadomolybdate method. The test is carried out simply by adding a single tablet to a sample of the boiler water.

In the test phosphates react with ammonium molybdate, in the presence of ammonium vanadate, to form the yellow phosphovanadomolybdate. The intensity of the colour produced in the test is proportional to the phosphate concentration and is measured using a Palintest Photometer.


A supplementary tablet may be optionally used for the removal of Silica interference.

Best Practice Advice for Testing

  • At low temperatures the rate of colour development in the test is substantially slower. Colour development should be carried out between 18 and 22°C. To ensure correct conditions for the test, the Tubetests tubes should be brought within this temperature range prior to use.
  • Samples drawn from boiler sampling points may be hot and contain particulate matter. Prior to analysis samples should be cooled to below 25°C and filtered through a Whatman No 42-filter paper.

EPA, Definition and Procedure for the Determination of the Method Detection Limit, Revision 2, Dec 2016.
IUPAC. Compendium of Chemical Terminology, 2nd ed. (the “Gold Book”).