RESULT AND DISCUSSION
The molybdenum blue method for the determination
of inorganic phosphate is a well-established method.
The blue color produced in this method is developed
by the reduction of 12-molybdophosphoric heteropoly
acid. Here the acidified solution of phosphate is treated
with ammonium molybdate that gives hetero poly acid
which is then reduced by hydrazine hydrate to give
phosphomolybdenum blue i.e. a blue color complex.
The reaction involved in the formation of molybdenum
blue can be given as:
PO4
3- + 12(NH4)2MoO4 + 24H+ → (NH4)3PO4.12MoO3
+ 21NH4
+ + 12H2O
(NH4)3PO4.12MoO3 + (N2H4.H2O) → molybdenum blue
The absorbance of thus formed phosphomolybdenum
blue was measured from 800 nm to 900 nm
spectrophotometrically and lmax was determined. The
wavelength at which maximum absorbance was observed
was considered as the lmax. On plotting absorbance
against wavelength, the wavelength of maximum
absorption (lmax) was found at 840 nm for the given
phosphate solution which is shown in the Figure 14.