Improvement of colorimetric microdetermination of sulfites in various foods by using the modified Rankine apparatus

Determination of traces of sulfites in various foods was attempted by use of the modified Rankine apparatus and para-rosaniline-formaldehyde colorimetry.Dimedone solution and sodium azide solution, which were used for elimination aldehydes and nitrites, must be prepared freshly before use. The effects of interfering substances in samples on the color reaction could be corrected for by subtraction of the sample blank which was obtained by adding hydrogen peroxide to the sample solution before color development.The detection limit of this method was 0.05μg/ml SO2 in test solution, corresponding to 0.5μg/g SO2 in food samples.Sulfites in 51 kinds of foods were determined. This colorimetric microdetermination analytical method could be applied to almost all foods.