b. Optimization of concentration of ammonium
molybdate
The concentration of ammonium molybdate also
plays a significant role in the formation of phospho
molybdenum blue complex. The effect of concentration
of ammonium molybdate on the on the formation of
phospho molybdenum blue complex was investigated
by varying the volumes (0.1 – 8) mL of ammonium
molybdate (2.5%), with the addition of 0.5 mL 10 N
sulphuric acid, 2 mL of phosphate solution (50 ppm)
and 1 mL of hydrazine hydrate (0.5M) in a 25 mL
volumetric flask and then made up to mark with distilled
water. After the time for maximum color development
the absorbance of these solutions were measured at
840 nm. The absorbance values indicated that the
solution of 0.20% ammonium molybdate appeared to
be more sensitive and hence was used throughout the
experiment for the determination of phosphate. The
plot of absorbance against concentration of ammonium
molybdate is shown in Figure 3