Ozone Residual Determination or Total Oxidant Determination by Iodometric Titration-Assisted Spectrophotometry

This publication introduces (a) ozone residual determination by iodometric titration-assisted spectrophotometry, (b) total oxidant determination by iodometric titration-assisted spectrophotometry, (c) traditional ozone residual determination by iodometric titration method, and (d) ozone residual determination by iodometric titration-assisted indigo colorimetric method. The new methods use identical chemical reagents required for ozone residue analysis by a historical standard iodometric titration method but need no titration step once a set of ozone calibration curves is established for subsequent spectrophotometric analysis. The basic principle involves the liberation of iodine from a potassium iodide solution in the presence of ozone residue (and other oxidants if the interferences are purposely not eliminated). After an acidification step for fixation of the ozone content (or total oxidant content, if intended for total oxidant analysis) in solution, the liberated iodine by ozone (and other oxidant, if included) produces a yellow color. The degree of color intensity is proportional to the original ozone concentration in water and can be measured spectrophotometrically or colorimetrically. The range of ozone concentration measurable is from 0.03 to 6.0 mg/L. The new method has a precision of ± 1% for ozone concentrations of 3 mg/L or greater. For total oxidant determination, the oxidant interferences are not eliminated, and the results will be expressed as total oxidant as “mg/L of O 3 ” . The total oxidant expressed as “mg/L of O 3 ” can also be converted to “mg/L of Cl 2 ” by mathematical calculation. The authors recommend that the traditional iodometric titration method be restored to be one of the Standard Methods for ozone residual analysis.