Phosphate-Vanadate-Molybdate
This method is based on APHA Standard Method 4500-P C. Description of the assay from the method: In a dilute orthophosphate solution, ammonium molybdate reacts under acid conditions to form a heteropoly acid, molybdophosphoric acid. In the presence of vanadium, yellow vanadomolybdophosphoric acid is formed. The intensity of the yellow color is proportional to phosphate concentration.
Reagents & Equipment
Colorimeter
Cuvettes
Vanadate-molybdate reagent, Labchem Cat # LC266002
1 mL variable micropipette
Colorimeter set-up
Wavelength: 470 nm. Use BLUE led (colorimeter RGB board).
Phosphate standard data: download a data file or prepare your own phosphate standard data
Before measuring samples, calibrate the colorimeter against water or a distilled water sample developed with vanadate-molybdate reagent as described below
Method
Transfer 1 mL of sample water into a clean cuvette.
Add 0.25 mL of vanadate-molybdate reagent and mix by pipetting up and down several times.
Wait at least 10 minutes for color to develop.
Place the cuvette with your sample into the colorimeter and click measure. The program will return the phosphate concentration in ppm.