The SO3 reacts with the water in the 80% IPA solution to form sulfuric acid.
SO3 (g) + H2O (l) → H2SO4 (aq)
The sulfuric acid then freely dissociates to 2H+ and SO4-2. The SO4-2 is then detected by either Ion Chromatography or titration. As SO3 is converted to H2SO4 there is no way to differentiate between the two.
Sulfur dioxide passes through the 80% IPA solution as the IPA inhibits it’s oxidation to SO3.
Sulfurous acid is produced when SO2 is bubbled through the hydrogen peroxide solution. The SO2 dissolves and reacts with water to form sulfurous acid:
SO2(g) + H2O(l) = H2SO3
The sulfurous acid is then oxidized to sulfuric acid by the peroxide:
H2SO3(aq) + H2O2(aq) = H2SO4(aq) + H2O(l)
The sulfuric acid then freely dissociates to 2H+ and SO4-2. The SO4-2 is then detected by either Ion Chromatography or titration.