Preparation of Sulfur Dioxide with Constant Low Concentration from the pH Controlled Sodium Hydrogensulfite Solution

A new method was developed for the generation of sulfur dioxide with constant low concentration (from 10 to 0.01 ppm). This method is based on the generation of sulfur dioxide from an aqueous solution of sodium hydrogensulfite with appropriate buffer agents. The pH of the solution was controlled by adding the buffer agents to it. Sulfur dioxide was generated by passing air through the surface of the solution. The generated gas was diluted with air of constant stream, passed through a purification bed. The concentration of the gas depended on pH, concentration, and temperature of the sodium hydrogensulfite solution. The gas generation from the solution began at pH 7.0, and generation of a large amount of gas occurred at pH 4.0. A logarithmic relationship between concentration of the solution and that of the generated gas in the air stream was found in a concentration range of sodium hydrogensulfite solution from 5×10 to 5×10² μg/ml. The temperature dependence on this method was much less than that on the permeation tube method and the variation of concentration of the generated gas with temperature was 0.02ppm/°C (at 20~30°C, 0.56ppm of SO₂). The concentration of the generated gas reached a constant value within about 40 min after starting of the air flow, and it remained constant at least during 6 hours. The range of variation of the generated gas was 2% at 0.56 ppm.