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Determination of orthophosphate ions using spectrophotometry

Dosing principle

In an acidic medium, orthophosphates form a complex with sulfomolybdic ions, the reduction of which by ascorbic acid leads to the formation of a blue-colored complex with a maximum absorption at 830 nm.

Illustration of a standard range for the determination of orthophosphates. 6 tubes contain a blue colored liquid with an increasingly pronounced coloration.

The phosphate content is expressed in mg.L-1 of PO43- or of P2O5:
1 mg.L-1 PO43- = 0.747 mg.L-1 P2O5 = 0.326 mg.L-1 P

Warning pictogram
Precautions for use: Filtering the water before dosing is preferable since the presence of suspended matter is capable of falsifying the colorimetric measurement.
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