Rapid microstill determination of free and total sulfite in wine with conductimetric detection

The development and optimization of on-line microdistillation for free and total sulfite (S(IV)) in grape juice and wine is reported. The microstill used both heat and an air stream to separate sulfur dioxide from the wine samples; the distillation product was captured in a peroxide solution, and converted to sulfuric acid, mirroring accepted industry practice. Measured from 1 to 300 mg L⁻¹ as SO₂ by conductance, sample throughputs of 60 h⁻¹ for free and 20 h⁻¹ for total sulfite were achieved. Data for bound S(IV) emphasises the slow kinetics of release reactions in some wines. The microstill method is more efficient for total sulfite than the accepted manual technique. Good correlation was found between the microstill and manual methods under specified control conditions.