The establishment of potential age markers of Madeira wine is of paramount significance as it may contribute to detect frauds and to ensure the authenticity of wine. Considering the chemical groups of furans, lactones, volatile phenols, and acetals, 103 volatile compounds were tentatively identified; among these, 71 have been reported for the first time in Madeira wines. The chemical groups that could be used as potential age markers were predominantly acetals, namely, diethoxymethane, 1,1-diethoxyethane, 1,1-diethoxy-2-methyl-propane, 1-(1-ethoxyethoxy)-pentane, trans-dioxane and 2-propyl-1,3-dioxolane, and from the other chemical groups, 5-methylfurfural and cis-oak-lactone, independently of the variety and the type of wine. GC Â GCToFMS system offers a more useful approach to identify these compounds compared to previous studies using GC-qMS, due to the orthogonal systems, that reduce coelution, increase peak capacity and mass selectivity, contributing to the establishment of new potential Madeira wine age markers. Remarkable results were also obtained in terms of compound identification based on the organized structure of the peaks of structurally related compounds in the GC Â GC peak apex plots. This information represents a valuable approach for future studies, as the ordered-structure principle can considerably help the establishment of the composition of samples. This new approach provides data that can be extended to determine age markers of other types of wines.KEYWORDS: Age markers, Madeira wine, HS-SPME, GC Â GC-ToFMS ' INTRODUCTION Madeira wine is a fortified Portuguese wine produced in Madeira Island over the last centuries and plays an important role in the economy of the Island. The peculiar characteristics of Madeira wines arise from the specific and singular winemaking process. The fermentation process is stopped by the addition of natural grape spirit in order to obtain an ethanol content of 18-22% (v/v). Some wines undergo aging in wood casks in cellars at temperatures up to 30°C, and humidity levels between 70 and 75%, while the majority of wines are submitted to a baking process, i.e., the wine is placed in large coated vats, and the temperature is slowly increased at about 5°C per day and maintained at 45-50°C during at least 3 months. After this treatment, the wine is allowed to undergo a maturation process in oak casks for a minimum of 3 years. Finally, some Madeira wines were submitted to an aging process, from a minimum of 3 to 20 years or even longer.1,2 The aging process in oak casks is fundamental for the Madeira wine's unique sensorial properties. During this period, several reactions and migration of molecules from the oak to wine can occur, 3,4 which depends on some parameters, such as grape variety, wine making procedure, and oak characteristics (geographical origin, species of oak, seasoning of the staves, toasting, and age of cask), 5-9 among others. The establishment of potential age markers is important to detect frauds and to ensure the authenticity of the wine. F...