Quantification of Chlorine Dioxide in Air

As a result of the reaction with chlorine dioxide, the solution of chlorophenol red discolored to white. The changes in the color of solutions were recorded on a spectrophotometer by the change in optical density at a wavelength of 571 nm in an optical cell with an optical path length of 5.00 cm. Different amounts of chlorine dioxide were added to the chlorophenol red solution. Calibration curve was plotted based on the obtained results.
The determination of the chlorine dioxide amount in the air was performed in an aspiration camera of nominal dimensions of 1 × 1 × 1 m and volume of 1.080 m³ (Figure 1b). It is made of cellular polycarbonate with a double-sided protective layer against ultraviolet light. The camera is equipped with two fans to homogenize the gas inside the camera, a humidity monitor and a thermometer to control humidity and temperature, respectively. The camera is connected in series with five modified Drexel absorbers filled with 10.00 ± 0.02 g of a working solution of chlorophenol red and a Kromschroeder BK-G 4 (Osnabrueck, Germany) volume meter of the passing gas for gas aspiration and absorption. Air was pumped out of the camera using an aspirator PU-4E (Moscow, Russia) for air sampling with an adjustable flow rate. The optimal aspiration rate was 5 L min⁻¹. The volume of gas passed through the chlorophenol red solution varied, considering the amount of chlorine dioxide released. When chlorine dioxide passed through the absorbers, the reaction with chlorophenol red occurred; this resulted in discoloration of the solution to white. Optical densities of each absorber’s chlorophenol red solution were obtained using a spectrophotometer. The optical density of the last solution remained consonant with the initial solution. The obtained total changes in optical density of each absorber solution were correlated to the calibration curve, and the chlorine dioxide concentration in the aspiration camera was determined using it.
The measurements of optical spectra were carried out on a Cary 100 Scan UV–Visible Spectrophotometer (Santa Clara, CA, USA) equipped with a thermostatted cell holder. Cooling or heating of the cell was accomplished by built-in Peltier elements, which allowed variation of the temperature of the optical cell containing the solution. The optical spectra were measured at 20 °C.