Although Mn VII has a strong disinfecting ability, Mn II does not. Cr VI is considered to be a carcinogen, while Cr III is an essential element in nutrition. 1 As unique biochemical roles of manganese and chromium, the determinations of individual amounts of the Mn II , Mn VII , Cr III and Cr VI in sample solutions are very important not only in environmental and biological research, but also in the control of industrial waste water. solution (3.5 mg ml -1 ) was prepared by dissolving 3.5 g of recrystallized KIO 4 in 1000 ml of water containing 6 ml of a saturated borax solution. g. A KI solution (33 mg ml -1 ) was prepared just before use, and stored in a brown bottle. h. A Na 2 SO 3 saturated solution. i. 3.1% Na 4 P 2 O 7 . j. HAc-NaAc buffer solution (pH=3.0). k. Ammonium molybdate solution (28%). l. Sulfuric acid solution (7 mol l -1 ), Fe 2 (SO 4 ) 3 solution (0.1 mol l -1 ) and NaOH solution (1 mol l -1 ). Unless otherwise specified, distilled water was used, and reagents were of analytical grade.
ProceduresAnalysis of mixed solution of Mn II , Mn VII and Cr III : known volumes (1 -7 ml) of the mixture solution containing 1.0 -500 µg Mn and 2.0 -350 µg Cr III were transfered to two 100-ml conical flasks and 1.0 -2.0 ml saturated sodium sulfite solution; then, 1.0 ml of 7 mol l -1 H 2 SO 4 was added to the solution. After about 1 min, the solution was boiled for 1 min to remove excess sulfurous acid. Then, 10 ml of the Na 4 P 2 O 7 solution was added in one flask, the pH was adjusted to about 3.0 with diluted NaOH solution at first, then to 3.0 with the