3. Procedures
3.1. Preparation of phosphomolybdenum blue complex A 30-ml volume of 0.1 M molybdenum(VI)solution is transferred into a 100-ml volumetric
flask, then 10 ml of 0.10 M potassium dihydrogenphosphate solution is added, followed by 10 ml of0.01% (w:v) sodium sulfide solution and 13 ml of
11.2 M HCl, in that order. The volume is completedwith water. The absorbance of the solutionis measured after 30 min at 814 nm against water
as a blank in a thermostatted bath at 2590.2°C.