Determination of Trace Sulfur Dioxide in Beer by Using Inhibition Fading Spectrophotometry

Based on the principle that sulfur dioxide can inhibit the fading of MB oxidized by potassium bromate in sulfuric acid medium, a method for rapid determination of trace sulfur dioxide in beer by inhibiting fading spectrophotometry was established. 1 mol·L^-1 sulfuric acid solution, 2×10^-4mol·L^-1 MB solution, 0.1 mol·L^-1 potassium bromate solution and sample solution treated with sodium hydroxide and sulfuric acid were added sequentially to the 25 mL colorimetric tube, the mixed solution was heated in a water bath at 50℃ for 3.0 min. The absorbance of the system (A) and the blank sample system (A₀) were measured at 660 nm, to obtain the difference in absorbance (ΔA, ΔA=A-A₀). The results showed that the mass concentration of sulfur dioxide had a linearity relationship with ΔA in the range of 0.04-0.4 mg·L^-1, with detection limit (3s/k) of 0.001 mg·L^-1. The recovery test was made on the actual sample by the standard addition method, giving recoveries ranged from 96.5% to 101%, and RSDs (n=11) of determined values were found in the range of 1.8%-2.8%. The proposed method was used in the analysis of cooked beer and draft beer, and determined values obtained were compared with those obtained by national standard method of GB 5009.34-2016, with relative error in the range of -1.5%-2.0%.