## 3 Results and Discussion
### Optimization of SPME Method  
In the present work, a method based on solid-phase microextraction in headspace mode and gas chromatography coupled with mass spectrometry (HSSPME-GC-MS) was developed for the identification of potential migrants in polymeric coatings. SPME is an easy, cheap, and clean method to use, although there is a for need further optimization in terms of equilibrium of experimental conditions such as heating temperature, extraction time, sample volume, concentration of volatiles, and sample matrix [23]. For that purpose, some parameters such as extraction time, equilibrium temperature, or the type of fiber were optimized. The effect of extraction temperature, extraction time, and desorption time was evaluated using the fiber DVB-CAR-PDMS. Firstly, the extraction time was optimized. Different times were tested (10, 30, and 60 min), keeping extraction temperature (40, 70, and 100 \({}^{\circ}\)C), equilibration time (2 min), and desorption time (10 min) fixed. Under these conditions the best results were found at 30 and 60 min of extraction because more peaks were identified and with a higher intensity, and there was hardly any difference between the two tested times, therefore, 30 min of extraction was selected. Once the time of extraction was optimized, the temperature was studied ranging from 40 to 100 \({}^{\circ}\)C. The difference in the sensitivity and the number of peaks detected was related with the increase of the temperature. The effects of temperature and extraction time were evident from the chromatograms obtained under the following conditions: 40, 70, and 100 \({}^{\circ}\)C for 10, 30, and 60 min. An increase in the peak chromatographic area was found, especially with the less volatile compounds at higher temperatures. [PERSON] et al. [24] reported that highly volatile compounds were not affected by desorption time and less volatile compounds needed more time to desorb. \begin{table}
\begin{tabular}{c c c c c c c} \hline
**Tr/min** & **Compound** & **CAS** & **Fl No.** & **MeOH** & **ACN** & **Hex** & **Hex: EtOH (3:1 _v/v_)** \\ \hline
10.56 & Benzoic acid methyl ester & 93-58-3 & 09.725 & x & & & \\
11.01 & Caprylic acid methyl ester & 111-11-5 & 09.117 & x & & & \\
12.97 & Adipic acid methyl ester & 627-93-0 & & x & & & \\
17.17 & Lauric acid methyl ester & 111-82-0 & 09.101 & x & & & \\
17.55 & Unknown compound (\(m/z\) 129) & & & x & & \\
18.07 & Diethyl phthalate \({}^{\star}\) & 84-66-2 & & x & x & x \\
19.92 & Ester & & x & & & \\
20.25 & Unknown compound (\(m/z\) 56) & & x & & & \\
21.71 & Thiophene & & x & & & \\
25.07 & Unknown compound (\(m/z\) 151) & x & & & & \\
25.56 & Adigate structure & x & x & x & x \\
25.65 & Adigate structure & x & x & x & x \\
30.43 & Unknown compound & x & x & x & x \\ \hline \end{tabular} \({}^{\star}\)Substances confirmed with a standard solution.  
\end{table} 
Table 2: Comparison of the most abundant detected compounds in sample BC04 using different extraction solvents. The next parameter that was optimized was the amount of the sample used, which was considered between 0.8 g and 2 g. Finally, the amount 0.8 g was chosen because larger amounts of sample did not lead to higher intensity of the chromatographic peaks. It is important to get a well-balanced compromise between sensitivity and extraction rate, particularly with respect to the extraction temperature, to achieve a careful optimization of each parameter. Best results and with the higher peak intensities were obtained for 30 min at 100 \({}^{\circ}\)C with 2 min of equilibration time and 10 min of desorption time. Selection of the Type of Fiber  
The selection of the fiber and SPME extraction conditions can affect the sensitivity and accuracy of SPME analysis. [PERSON] et al. [25] affirmed that using two-phase fibers (Carboxen-PDMS) seems to be more suitable for measuring low molecular weight compounds, whereas three-phase fibers (DVB-Carboxen on PDMS) appeared to be more appropriate for measuring high molecular weight compounds.