A fluorimetric method for the determination of atmospheric sulphur dioxide

A novel fluorimetric method has been developed for rapid determination of atmospheric sulphur dioxide with fluorescein as a fluorogenic reagent (λ_ex = 485 nm, λ_em = 515 nm) at pH 5.6 ∼ 6.0. In weak acidic medium, iodine reacted with fluorescein to produce a non-fluorescence species and cause the fluorescence quenching. However, this fluorescence quenching effect was largely decreased in the presence of SO₃^2- due to the reaction between iodine and SO₃^2-. Thus, the fluorescence intensity of fluorescein-I₂ system enhanced when SO₃^2- was added. The calibration graph is linear over the range 25 ∼ 150 μg/L SO₃^2-. The detection limit is 8.7 μg/L SO₃^2-. The method is rapid, sensitive and simple, it has been applied to the determination of atmospheric sulphur dioxide with satisfactory results.