# Development and Optimization of a SPME-GC-FID Method for Ethanol Detection
## 3 Results
### SPME Fiber Selection  
The choice of SPME fiber can have a significant impact on the extraction efficiency and selectivity of the analyte. Factors such as fiber coating material, fiber diameter, and fiber length can all influence the performance of the SPME fiber. The experiment's first phase focused on selecting the most effective fiber coating for extracting ethanol from a standard solution of 100 mg/L of ethanol. In this first experiment, a higher concentration of ethanol (10 times higher than the other experiments) was used in order to be sure that all fibers detected ethanol. Three different coatings were assessed based on their thickness and polarity, considering that thicker coatings may need more time to reach extraction equilibrium but can provide higher sensitivity due to the higher mass of extracted analytes. The fiber coatings for VOC extraction testing included 100 \(\upmu\)m PDMS (Polydimethylsiloxane), 75 \(\upmu\)m CAR-PDMS (Carboxen-Polydimethylsiloxane), and 50/30 \(\upmu\)m DVB/CAR/PDMS (Divinylbenzene-Carboxen-Polydimethylsiloxane). The standard solution was preincubated with the fibers before extraction. The results were analyzed based on the total peak area and the number of identified peaks (Figure 2).  
Among the different types of fiber coatings tested, the CAR/PDMS coating produced the highest peak areas in the SPME-GC-FID analysis. This suggests that the CAR/PDMS coating is the most effective at extracting ethanol from the sample. The peak area achieved with the CAR/PDMS fiber is roughly 77% greater than the peak area obtained with the DVB/CAR/PDMS fiber and approximately 98.5% higher than the peak area obtained with the PDMS fiber (* \(p\) < 0.05). The differences in extraction efficiency can be attributed to several factors, including the composition and properties of the fiber coatings. The CAR/PDMS fiber coating consists of a combination of Carboxen and Polydimethylsiloxane (PDMS). Carboxen is a porous carbon material that provides a high surface area and enhanced selectivity for analyte adsorption, while PDMS offers mechanical stability. The presence of Carboxen in the coating likely contributes to the higher extraction efficiency of ethanol due to its increased adsorption capacity for the analyte. The DVB/CAR/PDMS fiber coating includes divinyl benzene (DVB), Carboxen, and PDMS. DVB is a cross-linking  
Figure 2: Total peak area obtained by SPME-GC-FID analysis of ethanol (100 mg/L) using different fiber coatings. PDMS—100 \(\upmu\)m Polydimethylsiloxane, CAR/PDMS—85 \(\upmu\)m Carboxen/PDMS, Divinylbenzene/Carboxen/Polydimethylsiloxane (DVB/CAR/PDMS)—50/30 \(\upmu\)m DVB/Carboxen/PDMS (SPME extraction at 50 \({}^{\circ}\)C for 30 min, ethanol concentration 100 mg/L). Results are shown as the mean \(\pm\) SD (\(n=3\)). * \(p\) < 0.05 for CAR/PDMS when compared with the PDMS fiber, using the ANOVA test, followed by [PERSON]’s multiple comparisons tests.  
agent that enhances the stability and selectivity of the fiber coating. The addition of DVB in the coating composition may slightly alter the adsorption properties compared to the CAR/PDMS coating, potentially leading to slightly lower extraction efficiency for ethanol. The PDMS fiber coating consists solely of Polydimethylsiloxane, which is known for its nonpolar nature and compatibility with nonpolar analytes. While it can still extract ethanol, the lack of additional selectivity-enhancing components like Carboxen or DVB may result in lower extraction efficiency compared to the CAR/PDMS and DVB/CAR/PDMS coatings. In summary, the higher peak areas observed with the CAR/PDMS fiber coating compared to the DVB/CAR/PDMS and PDMS fibers can be attributed to the presence of Carboxen, which likely provides higher adsorption capacity and selectivity for ethanol. The composition and properties of the fiber coatings play a crucial role in determining their extraction efficiency, and the specific combination of Carboxen and PDMS in the CAR/PDMS coating proves to be advantageous for ethanol extraction in this study.