Analysis of chlorine-oxygen gas mixtures

Abstract

A simple, inexpensive method has been devised for the analysis of chlorine-oxygen gas mixtures using a flow system, i.e., a system in which the gas sample under test is injected into a mixing chamber and swept out by an inert carrier gas (N₂) to a chlorine trap and then an oxygen detector. Any chlorine gas (down to ca. 10 µl) present in the injected sample was found to be reduced quantitatively by the iodide present in the trap solution placed directly after the mixing chamber. The amount of triiodide formed as a result of this reaction was then determined spectrophotometrically. Removal of the chlorine by the iodide trap allowed any oxygen (down to ca. 20 µl) present in the sample then to be detected using an oxygen membrane polarographic detector (O₂-MPD). In addition, a chemical system for the in situ generation of accurately known amounts of chlorine gas was developed and the wide range over which it can be applied (10 ml-10 µl) was demonstrated using the flow system. In the chemical system, accurately known amounts of Ce^IV ions were injected into a strong brine solution (2 mol l^–1) to which a small amount of thermally activated RuO₂.xH₂O had been added. The thermally activated RuO₂.xH₂O acted as a redox catalyst for the quantitative reduction of the injected Ce^IV ions by the chloride ions via the reaction 2Ce⁴⁺+ 2Cl^–→ 2Ce³⁺+ Cl₂. Interestingly, in the absence of brine, this chemical system will generate oxygen via the quantitative reduction of the injected Ce^IV ions by water, i.e., 4Ce⁴⁺+ 2H₂O → 4Ce³⁺+ 4H⁺+ O₂. As a result, it can also be used to generate accurately known amounts of oxygen and chlorine. This chemical system provided a useful method for calibrating the flow system for the accurate determination of small amounts of chlorine (<1 ml). The problems associated with handling small amounts of chlorine gas for calibration purposes are also discussed in the paper.