Simplified method for free SO₂ measurement using gas detection tubes

The classic Monier-Williams method for free sulfur dioxide (SO₂) measurement in wines was modified using inexpensive SO₂detection tubes developed for the mining industry. An acidified wine sample was treated with an antacid tablet to evolve CO₂in situ and the gas flow directed to a commercial SO₂detection tube. The length of tube that changed color was proportional to the original free SO₂concentration. Initial calibration of the tubes was performed in model wines using aeration-oxidation (A-O) as a reference method. Using a 20 mL sample, the SO₂tube method achieved a linear response from 5 to 40 mg/L. Accuracy was evaluated by measuring free SO₂concentrations in 16 wines (seven whites, nine reds) by both the SO₂tube and A-O reference methods. Free SO₂concentrations for individual wines measured by each method were within ±2 mg/mL and the RMSE was 0.89 mg/L. The limit of detection of the SO₂tube method was 3.3 mg/L in wine. The SO₂tube method has several advantages over A-O, including requiring less time per analysis and no specialized glassware or equipment. The major consumable cost is the detection tubes, which can be conserved in exchange for precision by using smaller sample sizes.