Studies on the determination of dissolved oxygen in water

Studies on the decomposition rates of the Mn(III) complex of cyclohexanediaminetetra-acetate (DCTA) in light and in darkness have shown that this complex is more stable than the one derived from ethylenediaminetetra-acetate. The optimum pH range for the determination of dissolved oxygen by means of the Mn(III)-DCTA complex is found to be between 3 and 4. The absorbance of this complex is independent of the amount of DCTA used (in the range 0.2-1.0 g) with water samples containing a maximum of 3.2 ppm of dissolved oxygen. Significant interferences are caused by the presence of CO(2-)(3), HCO(-)(3), S(2)O(2-)(3), PO(3-)(4), I(-), NO(-)(2), SO(2-)(3), Ca(2+), Fe(2+) and Fe(3+) at 500 times the oxygen concentration.