Gas chromatography-mass spectrometry strategies for the accurate and sensitive speciation of sulfur dioxide in wine

Abstract Understanding the chemistry of wine oxidation requires the accurate and sensitive quantitative determination of the most important molecular species which SO 2 can form. An analytical strategy based in three independent static headspace GC–MS determinations is proposed in order to obtain information about the total, nominally free and truly free levels of SO 2 . Nominally free forms are directly determined after sample acidulation, total forms require the previous incubation at 100 °C, and truly free forms are determined after preconcentration of the headspace of the undisturbed sample in an alkaline solution. The two first determinations provide results equivalent to those reported by the aeration-oxidation (A-O) method, with lower limits of detection (1 mg L −1 ) and better repeatabilities ( 2 , which suggests that free SO 2 determined by any method using previous acidulation includes at least two different species of SO 2 , which may have different antioxidant behavior.