Determination of free and total sulfur dioxide in wine samples by vapour-generation inductively coupled plasma-optical-emission spectrometry.

Sulfur dioxide (SO(2)) is used as a preservative and stabilizer in wine production to prevent undesired biochemical processes in the must and the final product. The concentration of SO(2) is restricted by national regulations. There are two main forms of SO(2) in wine-free (inorganic forms) and bound (fixed to organic compounds, e.g. aldehydes). Iodometric titration is commonly employed for determination of SO(2) concentration (either by direct titration or after pre-separation by distillation); other techniques are also used. In this work inductively coupled plasma-optical-emission spectrometry with vapour generation was used for determination of free and total SO(2) in wine. Gaseous SO(2) is released from the sample by addition of acid and swept into the ICP by an argon stream. The intensity of the sulfur atomic emission lines is measured in the vacuum UV region. Determination of total SO(2) is performed after hydrolysis of bound forms with sodium hydroxide (NaOH). Concentrations of acid for vapour generation and NaOH for hydrolysis were optimised. The method was used for determination of free and total SO(2) in red and white wine samples and results were compared with those from iodometric titration.