The test paper allows the rapid detection of sulphit and sulphur dioxide. The paper is used in food analyzing laboratories. The reaction is as follows:
2 IO₃^– + 5 SO₃^2– + 2 H⁺ -> 5 SO₄^2– + I₂ + H₂O
Sulphurous acid or sulphites reduce potassium iodate to free iodine. With starch, iodine gives a characteristic blue-black color. For a detection of sulphite with high sensitivity we recommend Sulfit Test paper (REF 90763).