## 4 Conclusions  
HS-SPME/GC\(\times\)GC-TOF-MS analysis, alone or combined with conventional HS-SPME/GC-MS, was shown to be an excellent analytical tool for differentiation of wines according to variety based on volatile aroma compound composition. It has also been proven that the additional separation efficiency enabled by the second chromatographic column in GC\(\times\)GC-TOF-MS analysis was crucial for the separation and identification of a very large number of volatile compounds, which would otherwise remain undetected by conventional GC-MS. This feature provided additional in-depth volatile profile information which was exploited for highly efficient white wine varietal differentiation. Such an outcome can be considered even more successful knowing that the number of varieties was relatively high while that of wine samples of each variety was relatively small, and that the investigated wines were characterized by high intra-varietal heterogeneity in terms of micro-locations and grape cultivation and winemaking parameters. The results of this study confirmed the unmatched power of monoterenes to discriminate wines according to variety, which was robust enough to be captured by uni- and multivariate statistics based on both GC-MS and GC\(\times\)GC-TOF-MS analysis data separately.  
**Supplementary Materials:** The following are available online at [[http://www.mdpi.com/2304-8158/9/12/1787/s1](http://www.mdpi.com/2304-8158/9/12/1787/s1)]([http://www.mdpi.com/2304-8158/9/12/1787/s1](http://www.mdpi.com/2304-8158/9/12/1787/s1)), Figure S1: Example of a contour plot obtained for Malvazija istarska monovarietal wine using HS-SPME/GC\(\times\)GC-TOF-MS. Colored areas represent more abundant volatile aroma compounds and blackdots represent less abundant and trace volatile aroma compounds, Table S1: Physico-chemical parameters in in Croatian monovarietal wines, Table S2: Concentrations (ug/L) of volatile aroma compounds found in individual Croatian monovarietal wines after headspace solid-phase microextraction followed by gas chromatography-mass spectrometry (HS-SPME/GC-MS) sorted by compound class, Table S3: Concentrations (ug/L relative to internal standard 2-octanol) of volatile aroma compounds found in individual Croatian monovarietal wines obtained by headspace solid-phase microextraction combined with comprehensive two-dimensional gas chromatography-mass spectrometry with time-of-flight mass spectrometric detection (HS-SPME/GC\(\times\)GC-TOF-MS) sorted by compound class.  
Conceptualization, IL.; methodology, IL. and U.V.; formal analysis, I.L. and S.C.; investigation, I.L. and S.C.; resources, I.L. and U.V.; data curation, I.L. and U.V.; writing--original draft preparation; I.L.; writing--review and editing, I.L. and U.V.; supervision, I.L. and U.V.; project administration, I.L. and U.V.; funding acquisition, I.L. and U.V. All authors have read and agreed to the published version of the manuscript.  
This research was funded by Croatian Science Foundation grant number UIP-2014-09-1194 and by the ADP 2017 project funded by the Autonomous Province of Trento.  
The authors would like to thank wine producers from Croatia for donating wine samples, [PERSON], [PERSON], and the panel for sensory analysis of wine from the Institute of Agriculture and Tourism in Porex, Croatia, for assistance in collecting and selection of wine samples, [PERSON] for assistance in collecting wine samples, and [PERSON] for technical assistance.  
The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.