When a variation of acid concentration 0.24 M, 1 M or 3 M HCl was made for the preparation of the sample along with varying concentration of KI (0.5% and 1%) being used for prereduction, it was found that 3 M HCl and 1% KI gave optimum result as shown in Table 2. However, a much higher concentration was used for the reduction earlier (Hering et al., 1997)