Semicarbazide hydrochloride as an absorbing reagent for the fixation of atmospheric sulphur dioxide

Semicarbazide hydrochloride is proposed as an efficient absorbing reagent for the fixation of atmospheric sulphur dioxide. The proposed reagent has an absorption efficiency of ca. 100%, is non-toxic and is readily available in a pure form. After absorption, the amount of sulphur dioxide is determined spectrophotometrically, using p-aminoazobenzene and formaldehyde in acidic medium. The pink dye has a maximum absorption at 505 nm. The interference of nitrogen dioxide is much less than in other reported methods. The method has been successfully applied to the determination of sulphur dioxide in environmental samples.