# Volatile Composition of Fortification Grape Spirit and Port Wine: Where Do We Stand?
## 4 Methodologies for the Characterization of Grape Spirits and Port Wines' Volatile Components
In fact, the extraction is one crucial step for the beverages' volatile composition analysis, as it should provide a representative composition of the sample [56; 57], including the highly volatile fraction, that can be lost in this step or may be co-eluted with the extraction solvent during the chromatographic analysis. SPME also has the advantage of allowing the determination of the more volatile components of the beverages that can potentially impact the aroma characteristics. In fact, SPME is an alternative to perform the sampling and extraction/desorption of VOCs, which does not require expensive instrumentation, and, at the same time, fulfils the necessary requirements for implementation of green chemistry principles in analytical laboratories [58; 59]. SPME is an extremely versatile technique, due to the vast number of fiber coatings available on the market that allow a broader extraction or a selective one, for targeting specifically the analytes of interest [60; 61]. As observed in Table 1, divinylbenzene/carboxoen/polydimethylsiloxane (DVB/CAR/PDMS) has been used for the extraction of VOCs from the headspace of grape spirits and Port wines [17; 26], and polydimethylsiloxane/divinylbenzene (PDMS/DVB) has been applied in combination with derivatization [27] (Table 1). As the DVB/CAR/PDMS and PDMS/DVB fibers extract via an adsorptive-type mechanism, the analytes interact primarily with the surface of the sorbent coating instead of partitioning into the entire coating and, therefore, the sensitivity of these fibers depend on other factors such as the surface area and porosity of the material [59; 62; 63]. Due to the porosity properties of the DVB, the PDMS/DVB fiber may represent some concerns for the analyte displacement and has difficulty extracting analytes with low molecular weight, which explains why it is used to extract VOCs after derivatization (Table 1). The DVB/CAR/PDMS fiber, which combines three materials, was developed to overcome the limitations of CAR/PDMS in the desorption of higher molecular weight analytes and difficulty of PDMS/DVB in extracting analytes with low molecular weights. The DVB/CAR/PDMS coating contains two adsorbents that are layered to extend the molecular weight range of analytes extracted with one SPME fiber, and the combination with the PDMS confers it with a bipolar character, which explains the selection of this fiber in several studies [17; 26; 50; 52], allowing the determination of a wide set of analytes, such as acids, alcohols, aldehydes, esters, terpenic compounds, volatile phenols, norisoprenoids, and furaldehydes. Targeted determination of Port wines' carbonyl compounds (combined with derivatization procedure) [15; 16] and esters [49] was performed using solid phase extraction (SPE), associated with HPLC [16] and GC-MS [15; 49]. Two solid sorbents, namely LiChrolut-EN [15; 49] and C18 [16], were used. These two sorbents are widely used due to their properties, i.e., the performance of LiChrolut-EN cartridges for polar organic substances was explained based on its large specific surface, and C18 (octadecyl silica gel) selective extraction was controlled through hydrophobic interaction. One-dimensional gas chromatography (1D-GC) has been used for the characterization of the volatile components of grape spirits and Port wine. Gas chromatographs equipped with flame ionization (FID) or mass spectrometry detectors with quadrupole (qMS) ion trap or triple quadrupole (TQ/MS) analyzers are usually employed. (Table 1). The FID detectors are significantly cheaper than the MS detectors, but the latter achieve lower detection and quantification limits. Moreover, commercial mass spectra databases are available for MS detectors, comprising an important tool for analyte identification, giving them a substantial advantage over GC-FID. Besides the library mass spectrum comparison and the possible co-injection of standards, there is another strategy to boost the putative identification of volatile components, namely the determination of linear retention indices (LRI).