Indirect determination of molecular chlorine by fourier transform infrared spectrometry.

Nowadays, Fourier transform infrared (FT-IR) spectrometry (both extractive and open-path techniques) is widely used for the detection of air pollutants because the method is fast, reliable, and nondestructive. It is capable of detecting simultaneously all compounds except non-infrared active homonuclear diatomic molecules. Molecular chlorine gas has many anthropogenic sources, including water treatment plants, chemical production facilities, ceramic brick industries, and paper production processes, and it can also be formed in marine environments by reactions with sea salt particles. Various sensors have been applied to detect chlorine, including chemical sensors based on semiconductor metal oxides. Mass spectrometry also can be used for the determination of halogen molecules at atmospheric pressure. A mist chamber and ion chromatographic detection has been employed to detect molecular chlorine indirectly at the parts per trillion (ppt) level. Spectroscopic techniques (e.g., ultraviolet (UV), Raman) are also capable of measuring molecular chlorine directly. An artificial chlorine cloud was investigated by Edner et al. by the differential absorption LIDAR (light detection and ranging) method. Fourier transform infrared spectrometry has already been used to detect a homonuclear diatomic molecule. Larsen and co-workers measured the concentration of oxygen in a gas cell by determining the concentration of ozone produced upon UV irradiation of the sample. The authors established a linear correlation between the concentration of oxygen in the original sample and the concentration of ozone produced by photolysis of the sample. The aim of the present work was to investigate whether it is possible to detect chlorine molecules by means of FT-IR spectrometry as predicted by Hanst. If successful, a new analytical method can perhaps be developed based on this investigation.