EQUIPMENT
1. Spectrophotometer with an infrared phototube for use at 880 nm with a light path of at least 2.5 cm (1 in)
2. Acid washed glassware
3. An analytical balance capable of weighing to 0.1 mg accuracy
REAGENTS
1. Sulfuric acid solution 5 N
2. Potassium antimonyl tartrate solution
3. Ammonium molybdate Solution
4. Ascorbic acid solution
5. Combined reagent
6. Standard phosphate solution