Use of potassium iodide as a chemical actinometer

Aqueous solutions of KI were examined for use as chemical actinometers to measure 254 nm (germicidal) radiation. Irradiation results in electron ejection from iodide such that aqueous electrons and iodine atoms are formed. In the presence of N2O, an electron scavenger, recombination of these two reactive species is eliminated and stoichiometric formation of triiodide occurs. The absorbance increase due to triiodide was followed and the quantum yield determined using either a radiometer or ferrioxalate actinometry to estimate the amount of energy absorbed by the KI solution. The quantum yield (phi) at 25 degrees C was determined to be 0.26 using radiometry, and 0.224-0.233 using actinometry, depending on the radiation conditions. The following expression was used to measure the incident fluence rate for 254 radiation at a given temperature T for irradiation over a time interval delta t (s) [formula: see text] At temperatures other than 25 degrees C, the temperature dependence of the quantum yield (0.004/degrees C) is taken into account by the term shown in the denominator. Because KI remains relatively blind to longer wavelengths such as those found in normal room light, measurements can be made in the presence of room light without having to work in a darkened room.