Using indigo absorbance to calculate the indigo sensitivity coefficient

Ozone has become an increasingly popular alternative to chlorine for disinf ecting drinking water. Unfortunately, standard methods for calculating ozon e are time-consuming and require labor-intensive calibration. Gordon et al offer a simplified method of calibrating indigo dye for measuring ozone. Th e method they describe is fast, easy to perform experimentally, and effecti ve. The indigo dye used to measure aqueous ozone concentration slowly decompose s. It must be calibrated frequently to give good ozone measurements. Gordon and colleagues hope to eliminate the confusion at some utilities and in so me research laboratories by demonstrating how and why indigo decomposes. Gordon acid colleagues provide a "simple" method to calibrate the indigo dy e that is expected to lead to better ozone results. The indigo method shoul d provide improved, more reliable ozone concentrations-which it is hoped wi ll result in better and more effective use of ozone.