Optimization of concentration of various reagents
for the determination of phosphate
a. Optimization of concentration of sulphuric acid
The intensity of the color of phospho molybdenum blue
complex is significantly affected by the acidity of the
solution. In order to achieve maximum absorbance,
the effect of concentration of sulphuric acid was
investigated by taking various volumes (0.1-1.0
mL) of 10 N of sulphuric acid, 2 mL of ammonium
molybdate (2.5%) , 2 mL of phosphate solution (50
ppm) and 1 mL of hydrazine hydrate (0.5 M) in a 25
mL volumetric flask. Then the solutions were diluted
and made up to the mark with distilled water and left for
35 minutes for maximum color development. After this
the absorbance of each solution was measured at 840
nm. The absorbance values indicated that the solution
of 0.20 N sulphuric acid appeared to be more sensitive
and hence was used throughout the experiment for the
determination of phosphate. The plot of absorbance as
a function concentration of sulphuric acid is shown in
Figure 2. The blue color of the solution is obtained only
in acidic medium. At high acidity the color intensity
decreases. This is mainly due to the reason that at high
acidity the formation of phospho molybdenum blue
complex decreases
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