A Capillary Electrophoresis Method for Measuring Free SO2 in Traditional and Rosé Style Ciders
Philip Ashmore, Thomas Collins,* and James Harbertson *Washington State University, 359 University Dr, Richland, WA, 99354 (tom.collins@wsu.edu)
The most commonly used approaches for quantifying free SO2 in ciders, the Ripper and aeration-oxidation (AO) methods, can overestimate the amount of free SO2 in the presence of weekly-bound adducts, particularly anthocyanin sulfonates in red-pigmented products. Recent attempts to rectify this issue include the use of headspace gas detection tubes (HS-GDT) and headspace gas chromatography with sulfur chemiluminescence detection (HS-GC-SCD). The HS-GDT method has a notably limited linear range and high detection thresholds, while the HS-GC-SCD method is costly, with relatively long run times. A capillary electrophoresis with direct spectrophotometric detection (CE-UV/vis) method was developed to provide an inexpensive, rapid, and sensitive alternative that requires minimal sample preparation. The resulting method was fast (6 min per injection, 4 min with manual replenishment of buffer vials), sensitive (LOD = 0.03 mg/L, LOQ = 0.8 mg/L), repeatable (average RSD = 4%), and exhibited excellent linearity (R2 = 0.9999) and linear range (3 to 100 mg/L free SO2). This method was compared to measurements taken by Ripper, AO, and pararosaniline method measurements by clinical analyzer, in both unpigmented and rosé-style ciders. The method agreed with results by Ripper and clinical analyzer methods in unpigmented ciders, but differed slightly from AO measurements (two-way analysis of variance [ANOVA], p = 0.004), while measuring significantly lower in rosé ciders than Ripper and AO (two-way ANOVA, p < 0.0001). The CE method provides a more accurate result in rosé ciders than the most commonly used techniques, is more rapid and repeatable, and requires less sample preparation..
Funding Support: Washington State University
