Indirect Spectrophotometric Method for Determination of Sulfur Dioxide

Abstract

An operationally inexpensive and satisfactory analytical procedure for sulfur dioxide is proposed. The reagent 3-methyl-1,2-cyclopentanodione dithiosemicarbazone has been used to determine trace amounts of sulfur dioxide indirectly using the reduction of Fe(III) to Fe(II) principle. In order to find the optimal conditions for SO₂ determination, properties of 3-Me-CPDT-Fe(II) complex such as its composition, stability and free energy change of formation have been determined. The best conditions for the complex formation such as standing time, pH, wavelength and the effect of interfering ions are described. The complex has been used with success in spectrophotometric determination of SO₂. The procedure can determine down to 0.63 μg and recoveries are better than 97.5%. The method is also suitable for determination of sulfur dioxide in the air provided that interfering gases such as H₂S and NO₂ are removed.