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Phosphate (Ortho) Test Kits

Visual Kits

Range MDL Method Type Kit Refill
2 - 30 ppm 2 ppm Vanadomolybdophosphoric Acid CHEMets K-8530 R-8515
0 - 120 ppm 5 ppm Vanadomolybdophosphoric Acid CHEMets K-8515 R-8515
0.0 - 1.0 & 1 - 10 ppm 0.05 ppm Stannous Chloride CHEMets K-8510 R-8510
10 - 100 ppm 10 ppm Stannous Chloride HR CHEMets K-8520D R-8510

Instrumental Kits

Range Method Type Kit
0 - 8.00 ppm (V-2000) / 0 - 5.00 ppm (V-3000 & Spectro.) Stannous Chloride Vacu-vials K-8513
0 - 80.0ppm Vanadomolybdophosphoric Acid Vacu-vials K-8503

The CHEMetrics test kits for the determination of Phosphate in aqueous solutions employ the the well-known Vanadomolybdophosphoric Acid and Stannous Chloride reagents, delivering sensitivity and accuracy in two minutes. Based on CHEMetrics patented Self-Filling Reagent Ampoule technology. Premixed. Premeasured. Precise. Each kit contains 30 tests. Visual and instrumental phosphate testing kit formats span low and high measurement ranges. CHEMets® and HR CHEMets® visual test kits use colour comparators for analysis while Vacu-vials® instrumental kits rely on CHEMetrics direct-readout photometers or spectrophotometers capable of accepting a 13-mm diameter round cell.

The Phosphate Vacu-vials test kits K-8503 and K-8513 can be used with a Hach DR900 Colorimeter in conjunction with the CHEMetrics DR900 Vacu-vials® Adapter, Cat. No. A-0215. No endorsement by Hach Company is implied or intended.

The Vanadomolybdophosphoric Acid Method

In test kits employing the vanadomolybdophosphoric acid method, phosphate reacts with ammonium molybdate under acid conditions and in the presence of vanadium to form a yellow-coloured product. Results are expressed as ppm (mg/l) PO4.

ASTM D 515-82, Phosphorous in Water, Test Method C.
APHA Standard Methods, 22nd ed., Method 4500-P C-1999.

Technical Data Sheet

The Stannous Chloride Method

Test kits employing this chemistry utilise a stannous chloride reduction. Phosphate reacts with ammonium molybdate and is then reduced by stannous chloride to form a blue complex. Results are expressed as ppm (mg/l) PO4.

To convert the PO4 test results to ppm Phosphate as P, simply multiply by 0.326. The V-2000 Multi Analyte Photometer has a choice of programs for the Phosphate test kit K-8513, both Phosphate as PO4 (0 - 8.00 ppm) and Phosphate as P (0 - 2.64 ppm). Please see page 5 of the V-2000 Operator’s Manual for further information.

APHA Standard Methods, 22nd ed., Method 4500-P D-1999.

Technical Data Sheet


High phosphate concentrations in surface waters may indicate fertiliser runoff, domestic waste discharge, or the presence of industrial effluents or detergents. Although phosphates from these sources are usually polyphosphates or organically bound, all will degrade to ortho- or reactive phosphates with time.

Phosphate measurement is used to control scale inhibitor and corrosion inhibitor levels in boilers and cooling towers. Both test methods described above measure reactive phosphate (a.k.a. ortho-phosphate), which will give a positive reaction prior to hydrolysis.

What is Phosphate?

Phosphate is a phosphorus-containing anion, salt, ester or functional group derived from a type of phosphoric acid. There are several types of phosphoric acid, the simplest and most commonly occurring of which is orthophosphoric acid (H3PO4), so named because it contains one functional phosphate group. Other less common phosphoric acids include pyrophosphoric acid, tripolyphosphoric acid, tetrapolyphosphoric acid and more. These are formed when two or more orthophosphoric acid molecules are joined into larger molecules by the removal of water. However, the term ‘phosphoric acid’ is used to denote orthophosphoric acid.

Phosphates can be either inorganic or organic (a.k.a. organophosphate) salts or esters. Phosphates include orthophosphate, oligophosphate, polyphosphate and cyclic polyphosphate which derive from their respective phosphoric acids. Commonly the term ‘phosphate’ refers to orthophosphate (PO43-), a phosphate with only one functional phosphate group, which is a derivative of orthophosphoric acid.

Phosphorus occurs naturally in rock formations in the earth's crust, usually as phosphate. Phosphorus is present in natural waters in three forms: soluble reactive phosphorus (SRP), soluble unreactive/organic phosphorus (SUP) and particulate phosphorus (PP). SRPs are mainly inorganic orthophosphate.

Phosphate ions occur in three forms:

  • PO43-, by removal of all three H+ ions (protons)
  • HPO42-, by removal of two H+ ions
  • H2PO4-, by removal of one H+ ion