Part 2: How to measure phosphorous
7. Use Spectrophotometric method to measure phosphorous
8. Put 5ml of ash solution to a 100ml volumetric flask, then add 25ml of vanadate-molybdate reagent.
9. Wait for 10 mins, determine absorbance of solution at the 420mm wavelength against blank sample
10. To make vanadate - molybdate solution:
11. Dissolve 20g of ammonium molybdate in 50degrees celcius of 400ml water, then let it cool down
12. dissolve 1g of ammonium vanadate in 300ml boiling distilled water and let it cool, after cooling add in 140ml of concentrated nitric acid while stirring
13. add molybdate solution in the acid solution while stirring it
14. Add distilled water to make solution into 1L