Phosphate/12P Tubetest

Test Method Technical Information


Tests For: Phosphate in Natural, Drinking Water and Wastewater
Tests Range: 0–12 mg/L P
Reagent Chemistry Used: Ascorbic acid/molybdenum blue
Basis of Test Method: Standard Method 4500-P-E, US EPA method 365.1, 365.3
Method Detection Limit*: 0.09 mg/L
Limit of Quantification**: 0.27 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

Phosphates are extensively used in detergent formulations, in food processing and in industrial water treatment processes. These phosphates may be in the form of orthophosphates or are broken down to orthophosphates in the process concerned. Agricultural fertilisers normally contain phosphate minerals. Phosphates also arise from the breakdown of plant materials and are found in animal wastes.

Phosphates can therefore enter water courses through a variety of routes particularly domestic and industrial effluents and run-off from agricultural land. Phosphate is an important control test for natural and drinking waters.

Whilst phosphates are not generally considered harmful for human consumption, they do exhibit a complex effect on the natural environment. Phosphates are associated with eutrophication of water and with rapid unwanted plant growth in rivers and lakes. Phosphates present in natural water pass through into drinking water supplies.
en over the range 0–1 mg/L N. The test can however be extended to cover the range 0–20 mg/L by a simple dilution technique.

The Palintest Tubetests Phosphate/12P test provides a simple method of measuring orthophosphate levels over the range 0–12 mg/L P.

Reagent Chemistry

In the Palintest Tubetests Phosphate/12P method, the phosphate reacts under acid conditions with ammonium molybdate to form phospho-molybdic acid. The compound is reduced by ascorbic acid to form the intensely coloured ‘molybdenum blue’ complex. A catalyst is incorporated to ensure complete and rapid colour development, and an inhibitor is used to prevent interference from silica. The reagents are provided in the form of a pre-dispensed tube and two tablets for maximum convenience. The test is simply carried out by adding a sample of the water and one of each tablet.

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”).