Determination of free and total diacetyl in wine by HPLC–UV using gas-diffusion microextraction and pre-column derivatization

Diacetyl (DC) is responsible for a buttery aroma in many fermented foods and beverages. The addition of sulphites is a well-known practice in wine making; the formation of DC–sulphite adducts reduces the free DC content lowering its sensorial perception. However, chemical modifications in wine composition during wine storage result in the release of bound DC. This work proposes an accurate determination of free and total DC (based in a hydrolytic chemical treatment aiming to break adducts) in wines using gas-diffusion microextraction (GDME) and analysis by high-performance liquid chromatography with spectrophotometric detection (HPLC–UV) applying pre-column derivatization with o-phenylenediamine (OPDA). The proposed methodology was successfully applied in wines showing that free DC/total DC ratios varied from 30% to 60%. DC presence in wine samples was also confirmed by mass spectrometric (MS) analysis of the derivatives. Furthermore, the structure of the derivative, dimethylquinoxaline, was characterized by this technique.