Estimation of Ozone

Ozone in small quantities is usually estimated by the oxidation of potassium iodide, the gas being passed through a neutral or alkaline solution of the salt. With an alkaline solution there is less danger of the loss of iodine, and in any case the solution must not be acidified until after the ozone treatment or the results will be high. The extent of the oxidation is determined by acidifying and then titrating the liberated iodine with thiosulphate in the usual way.

In acid solution, potassium bromide is oxidised quantitatively by ozone yielding an equimolecular proportion of bromine, and this reagent can therefore be used for the estimation of dissolved ozone in the presence of hydrogen peroxide.

Ozone can also be estimated by slowly passing the gaseous mixture through sodium hydrogen sulphite solution and titrating the unchanged sulphite with iodine, or by the gravimetric process of absorbing the gas in oleic acid or linseed oil and measuring the increase in weight.