Spectrophotometric determination of dissolved oxygen in water with indigo carmine

Abstract

An analytical method of a small amount of dissolved oxygen in deaerated water has been established by measuring the color development between oxygen and indigo calmine. Ordinally the color produced by the reaction of oxygen with reagent is compared with the standard colors by eye. Although very rapid and sensitive, this method is not accurate. This paper describes the results obtained by spectrophotometric studies, and the application to the determination of oxygen dissolved in the feed water of a high pressure boiler or an atomic power plant (BWR). The analytical procedure is as follows. After taking a sample water in a sampling vessel, a reagent in a buret of the vessel is introduced into the vessel by opening a cock. After developing a clolr, the absorbance was messured with a Hitachi spectrophotometer (model 139) by setting a special cell holder. The absorption wavelength of the oxidized indigo carmine are 510, 555 and 610 nm. The most suitable wavelength to determine a small amount of oxygen is 555 nm. To prepare a calibration curve, known amounts of oxygen were added by electolyzing the sample water. A linear calibration curve was obtained within a range of less than 80 ppb oxygen. The coefficients of variation were 15.7, 8.1 and 2.4 for 3.5, 13 and 50 ppb oxygen, respectively. The analytical values obtained from the feed water in a power plant were in good agreement with those obtained by Winkler-amperometry (JIS B 8224). © 1976, The Japan Society for Analytical Chemistry. All rights reserved.