###### Abstract
Recently, the demand for more sustainable, solvent-free, and straightforward techniques has increased, leading to the development of solid phase microextraction, SPME [22]. SPME can be performed in two modes: headspace (HS) or direct immersion (DI). HS-SPME is the most frequently used, as it preserves the lifetime of the fiber [23]. This technique, developed in the 1990s, is highly advantageous because it does not require the use of organic solvents, and it is a simple and fast technique; so, it is promising for the analysis of varietal volatile compounds [24]. Due to the complexity of the volatile composition of grapes and the trace levels of those compounds, it is crucial to make use of advanced analytical techniques that enable the separation and detection of the compounds from the whole matrix (grapes). Indeed, gas chromatography is the most frequently used analytical technique for this purpose. However, varietal volatile compounds from grapes are structurally very similar; thus, the occurrence of the co-elution phenomenon is commonly observed, hampering unequivocal detection by means of only unidimensional GC [25]. Thus, comprehensive two-dimensional gas chromatography (GC\(\times\)GC) has emerged as a powerful analytical technique for the analysis of complex samples and as a potential alternative to one-dimensional separation [26]. This technique is based on the use of two columns coated with different stationary phases and connected through an interface called a modulator [27]. According to [PERSON] et al. 's 2011 study [28], the GC \(\times\) GC provides more confidence in qualitative and quantitative analyses, a high separation efficiency, a good ability to detect minor analytes, and information about the sample and its composition. In fact, modulation is one of the crucial steps in GC \(\times\) GC and can be performed using cryogenic modulators or flow modulators. During the modulation period, the modulator is responsible for collecting the fraction that comes out of the first column, focusing it, and injecting the fractions into the second column [29; 30]. The modulation range of flow modulators is significantly larger compared to that of thermal modulators; for example, eluates containing compounds with vapor pressures corresponding to C\({}_{1}\) to C\({}_{40}\) alkanes can be modulated [31]. Other advantages of using flow modulators compared to cryogenic modulators are better repeatability, no restrictions on sample volatility, and lower maintenance costs; moreover, the use of flow modulators does not require cryogen liquid to carry out the modulation [32; 33]. Thus, the GC \(\times\) GC system requires the coupling of detectors that can provide high detection efficiency, low noise, and quick response with small sample volumes over a broad dynamic range [25]. Recently, Mass Spectrometry (MS) has emerged as a powerful technique, providing information about the chemical identity of molecules in complex matrices. The combination of HS-SPME with GC \(\times\) GC-TOFMS techniques allows for the analysis of complex samples, even if the compounds of interest are present in trace amounts, as is the case of varietal volatile compounds in grapes [34; 35]. To the best of our knowledge, the use of flow modulator-based GC \(\times\) GC-TOFMS for the determination of varietal volatile compounds in grapes has never been explored. This innovative study intends to achieve a deep knowledge of the volatile profile of Trincadeira, Cabernet Sauvignon, Syrah, Castelao, and Tinta Barroca grape varieties, mainly focused on the composition of monoterenes, sesquiterpenes, and C\({}_{13}\)-norisoprenoids. Additionally, this work will also assess the usefulness of flow modulator-based GC \(\times\) GC-TOFMS on the tracing signature of the grape varieties under study.