Hi, Snigdha,

This is something which can be simply tested in the lab. In order to verify whether this vanadomolybdate method is appropriate to detect concentrations of 60 mg/L orthophophate, just prepare a number of standards with known concentration of orthophosphate (e.g.: 1 , 5 , 10, 25 , 50, 75 mg/L). Then, measure the absorbance of each standards, and make a plot of the absorbance versus the concentration of orthophosphate in your sample. This should yield a linear trend. If the orthophosphate concentration becomes too high, there will be not longer a linear relationship between absorbance and concentration.

If this would be the case, you can consider to search for an alternative colorometric method but, more easily, you can just dilute the sample with deionized water so that the concentration is sufficiently low to be dectable with the vanadomolybdate method.

Dear Snigdha,

The orthophosphate anion reacts with ammonium molybdate in an acid medium to form phosphomolybdic acid. This acid is reduced by ascorbic acid in molybdenum blue whose absorbance at 660 nm is proportional to the concentration of phosphorus.

You can use the automated ascorbic acid colorimetric method with appropriate dilutions.

With my best regards

Prof. Bachir ACHOUR

For orthophosphate, Ascorbic acid method is appropriate . This is spectrophotometric method. In view of accuracy,Standard solutions and calibration part is very important

If your sample have a high concentration in phosphate and you dilute it, make some test with spiked samples in order to evaluate potential effects of dilution or matrix effects.

Thank you all. All the answers were informative and useful.

Dear Snigdha Goel

There are many ways of measuring high levels of phosphate concentrations in wastewater such as chemical titration ( laboratory) and you can use 'Atomic Absorption Spectrometer ' ext...

Regards

I agree with Niels Wardenier answer