New Method for Rapid Determination of Free Sulfur Dioxide in Wine and Cider

A recent study published in Journal of Chromatography A introduced a new method for the determination of "true" free sulfur dioxide (SO₂) in wine and cider using capillary electrophoresis with direct UV-visible spectrophotometric detection (CE-UV-vis) (1).

Minimal sample preparation is required for this method, and it allows for the analysis of samples at pH 3.0, which prevents artificially high values in pigmented samples. The CE method was validated in both unpigmented and pigmented wine and cider samples. The study concluded that the new method was found to be fast, sensitive, and repeatable.

The study compared the CE method to three conventional methods for measuring free SO₂, including the Ripper method, Aeration-Oxidation (AO), and pararosaniline by discrete analyzer (DA). Although some statistically significant differences were found between the four methods in unpigmented model solutions and samples, the values generally agreed.

However, in the presence of anthocyanins in model solution and red wines, free SO₂ values found by CE were significantly lower than the other three methods. The difference in values found by Ripper and CE correlated strongly with anthocyanin content and even more strongly when accounting for polymeric pigments.

The results in red ciders differed from those in red wines. Although the CE method measured significantly lower free SO₂ values than the other three methods, the difference in free SO₂ values measured by CE and Ripper correlated more closely with anthocyanin concentration than absorbance due to bleachable pigment. The CE method was found to be rapid (4 min/injection), sensitive (LOD = 0.5 mg/L, LOQ = 1.6 mg/L free SO₂ in wine, 0.8 and 2.8 mg/L, respectively, in cider), robust, and repeatable (average RSD = 4.9%) and did not suffer from the issue of over-reporting free SO₂ in pigmented samples often observed with currently accepted methods.

The study's authors believe this new method offers significant benefits for wine and cider makers. The method is faster, more sensitive, and more accurate than conventional methods, making it an attractive option for winemakers who need to monitor free SO₂ levels in their wines regularly. Additionally, the CE method does not require large quantities of reagents or complex sample preparation, which should reduce costs and improve efficiency.

Overall, this new method for the determination of free SO₂ in wine and cider using CE represents a significant step forward for the wine and cider industry. Its speed, sensitivity, and accuracy make it a valuable tool for winemakers looking to ensure their wines meet quality standards and remain stable over time.

Reference

(1) Ashmore, P. L.; Valdez, F.; Harbertson, J. F.; Boulton, R. B.; Collins, T. S. Rapid determination of free sulfur dioxide in wine and cider by capillary electrophoresis. J. Chromatogr. A. 2023, 1695, 463936. DOI: 10.1016/j.chroma.2023.463936