4. Optimization
4.1. Effect of concentration of ammonium molybdate solution
The effect of ammonium molybdate on the color intensity of
the reduced phosphomolybdate complex at constant volumes of
0.5 ml of 0.25N sulfuric acid, 1 ml of 50ppm phosphate, 0.5 ml of
2% thiourea was examined with various volumes of (0.25–2 ml)
of 5.54×10−3M molybdate solution per 10 ml of total solution.
Absorbances of the solutions were measured at 840 nm. The results
obtained are shown in Fig. 2, that are accounting for the maximum
absorbance value for the solution containing 0.5 ml of
5.54×10−3M ammonium molybdate solution. Above that volume of molybdate solution, the absorbance of the solution was
decreasing; therefore, 0.5 ml of 5.54×10−3M ammonium molybdate
solution was used in the analysis of samples for phosphate