Absorptiometric determination of low oxygen concentrations in power-station waters. Part I. Manual method

Abstract

A simple, fast method for determining low concentrations of oxygen in power-station waters has been developed, based on the reaction of dissolved oxygen with the leuco-base of methylene blue to give a soluble blue oxidation product the absorbance of which is a function of the oxygen concentration.

A special glass cell has been devised, which acts sequentially as a sample-collection vessel, a reaction vessel and a spectrophotometric cuvette. The cell design permits the easy addition of the leuco-base and also the air-saturated water used for calibration. A novel technique of “zero-time extrapolation” for the determination of the reagent/cuvette blank circumvents the difficulty of making this measurement with oxygen-free water.

The calibration graph is linear up to 50 µg l^–1, but satisfactory measurements may be made up to 100 µg l^–1. The criterion of detection is approximately 1.0 µg l^–1 with standard deviations ranging between 0.4 and 1.7 µg l^–1, depending on the concentration. The analysis time is 5–10 min for a single determination.

Iron(II) and copper(II) ions are the only ions likely to be present in boiler waters that cause serious interference and these must be removed before analysis by passing the water sample through a cation-exchange column.