## 3 Detection of EVOO and VOO Adulteration by Gas Chromatography  
A common technique used by many researchers is solid-phase microextraction (SPME) accompanied with gas chromatography, which allows the characterization and quantification of the volatile composition of olive oil. SPME is a routine, low-cost, easy and efficient technique developed by [PERSON] and [PERSON] in 1990 [PERSON] and [PERSON] in 1990 [PERSON] and [PERSON] (1990). The technique occupies the use of a fiber coated with an extracting phase which can be solid or liquid, able to extract volatile and semi-volatile compounds from a sample. The sample is exposed to the fiber under steady temperature and stirred for a certain time, until the extracted compounds are absorbed by the fiber to the maximum of their concentration. Then, the SPME fiber can be directly injected into the GC system, where helium carries the volatile compounds into the capillary column and analysis of the sample begins (Table 2). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Authors** & **Method** &
\begin{tabular}{c} **Collection of Volatiles** \\ **(e.T.; i.e.t.)*** \\ \end{tabular} & **SPME Fiber Type** & **Focus** & **Chemometrics** \\ \hline \hline \multicolumn{6}{c}{**Detection of Adulteration**} \\ \hline
[47] & SPME-MDGC & 70 °C &
\begin{tabular}{c} Detection of adulteration of \\ EVOO with hazellum oil (based \\ on filterbene) derived from \\ unroasted hazelnuts \\ \end{tabular} & - \\
[48] & SPME/GC-MS & \begin{tabular}{c} 50 °C \\ - \\ 15 min \\ \end{tabular} & \
\begin{tabular}{c} **SPME Fiber Type** \\ - \\ 15 min \\ \end{tabular} &
\begin{tabular}{c} **Focus** \\ **(e.T.; i.e.t.)*** \\ \end{tabular} & **Chematometrics** \\ \hline \hline \multicolumn{6}{c}{**Discrimination According to Geographic Origin**} \\ \hline
[49] & GC- & 40 °C & \
\begin{tabular}{c} Geographical discrimination of \\ EVOO \\ \end{tabular} &
\begin{tabular}{c} PLS and LDA \\ analysis \\ analysis \\ \end{tabular} \\
[50] & GC-SPME & 10 min & \
\begin{tabular}{c} DVB/CAR/PDMS \\ 40 min \\ \end{tabular} &
\begin{tabular}{c} Geographical discrimination of \\ VOOs based on phenols and \\ volatile compounds \\ \end{tabular} & Anova and PCA \\
[51] & SPME/GC- & 40 °C &
\begin{tabular}{c} Volatile compounds as markers \\ for the geographical \\ differential of Spanish EVOO \\ \end{tabular} & PCA, LDA and SLDA \\
[52] & HS-SPME-GC- & 70 °C & \
\begin{tabular}{c} Geographic authentication of \\ EVOO based on sesquiterpen \\ profile \\ \end{tabular} &
\begin{tabular}{c} PCA, PLS-DA \\ analysis. \\ \end{tabular} \\
[53] & HS-SPME/GC- & 40 °C &
\begin{tabular}{c} Geographical characterization of \\ Italian VOO based on volatile \\ analysis \\ \end{tabular} & ANOVA, DA, PCA \\
[53] & GC-MS & 30 min &
\begin{tabular}{c} Profile \\ \end{tabular} & ANOVA, PCA and \\
[54] & HS-SPME, & 25 °C &
\begin{tabular}{c} Characterization of virgin olive \\ oil according to their geographical \\ origin \\ \end{tabular} & ANOVA, PCA and \\
[55] & SPME/GC- & 60 min & DVB/CAR/PDMS & Authenticity of VOO (labeled as \\ FID & 90 min & \
\begin{tabular}{c} PDO) with commercial EVOO \\ \end{tabular} &
\begin{tabular}{c} ANOVA, PCA and \\ HCA analysis \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Gas chromatography and volatile profile to evaluate authenticity of EVOO and VOO. [PERSON] et al. (2006) [47] studied the adulteration of EVOO with hazelnut oil using various techniques based on its volatile fraction, among which SPME-multidimensional gas chromatography (SPME-MDGC). For the experiment, a Divinylbenzene/Polydimethylsiloxane (PDMS/DVB) fiber was used. Authors preferred to label an EVOO as adulterated only when both R and S enantiomers of filbertone were identified after an analysis of the results. Detection of adulteration was achieved to a range of 7-25% for hazelnut oil. One of the most important findings of this study was the fact that the hazelnut oil used was derived from unroasted raw material.