Sulfur Dioxide Content of Wine. Ii. Acid-Bleached Fuchsin-Formaldehyde Colormetric Method

¹ Department of Food Technology, University of California, Berkeley

Several factors affecting the use of acid-bleached fuchsin for the colorimetric determination of sulfur dioxide were investigated. Of these factors the concentration of sulfuric acid in the reagent had the greatest effect on its sensitivity. For use with the Klett photoelectric colorimeter, the undiluted reagent limited the range of sulfur dioxide content that could be determined and both the range and reproducibility of the reagents could be improved by 1:5 dilution after development of color. The Grant reagent, containing added formaldehyde was not as stable as the Steigman reagent and this was simplified by addition of weighed amounts of fuchsin after wetting with alcohol. The reagent so prepared was stable for several months. The results obtained were noticeably influenced by conditions of use but when the order of addition of the sulfur dioxide solution and reagent and condition of color development were controlled reproducible results could be obtained. As applied to wine however the sulfur dioxide content

determined colorimetrically gave appreciable higher values for free and lower values for total sulfur dioxide content.