# Optimization of HS-SPME-GC-MS for the Determination of Volatile Flavor Compounds in Ningxiang Park
## 3 Results and Discussion
### Influencing Factors on GC-MS Analysis
#### 3.1.2 Effect of Extraction Head on VFCs  
According to the coating material and extraction head thickness, the test results of four extraction heads were compared to identify the best extraction head for identifying VFCs in Ningxiang pork. The extraction head of the Gray50/30 model, whose coating materials included DVB, CAR, and PDMS, had the best detection effect, according to the findings of the detection of the total ion chromatogram (Figure 1a, Table 1). The number of chemicals discovered decreases with the structural richness of the coating (Figure S2). The analyte typically contains many volatile substances that the extraction head's single structure cannot entirely adsorb. The main application scope of DVB/CAR-PDMS is volatile and semivolatile aroma substances, indicating that Ningxiang pork was rich in aroma substances after heat treatment. In addition, the PDMS coating (Red100) is mainly used to adsorb nonpolar substances in combination with CAR and DVB materials (the extraction head is Gray50/30), which significantly increases the type and quantity of adsorbed substances. The volatile compounds of Ningxiang pork after heat treatment accounted for a sizable proportion of medium polar substances. Blue65 detected significantly more substances than Black75 (Figure 1a), but the total amount of adsorbed substances was opposite (Figure 1b), probably because the volatile substances with larger molecular weight could not be adsorbed by CAR/PDMS after the heat treatment of Ningxiang pork. Additionally, the covering of Black75 is thicker than that of Blue65, which leads to more species being adsorbed.  
Figure 1: (**a**) The number of different kinds of volatile flavor compounds detected by different extraction heads; (**b**) the total amount of volatile flavor compounds detected by different extraction heads; (**c**) the number of volatile flavor compounds detected under different heat treatment time conditions; (**d**) the total amount of volatile flavor compounds detected under different heat treatment time conditions.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Extractor Model** & **Number of Peaks** & **Total Peak Area** \\ \hline DB-5-30 m & 44 & 14,496,024 \\ DB-5-60 m & 67 & 26,231,349 \\ HP-88-100 m & 23 & 4,366,547 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Comparison of column results.  
As in previous studies on the extraction of VFCs from pork [34; 41], beef [42], and mutton [43; 44], the best selection of extraction head is still the Gray50/30 model made of DVB/CAR-PDMS. Furthermore, the choice of extraction head for this model is consistent with the results of [PERSON]. [PERSON]'s choice of extraction head model [37]. Therefore, the characteristics and thickness of the coating materials have a significant impact on the selectivity and enrichment of VFCs. We should select the coating materials of the traction head according to the standards of similarity and compatibility, so as to better adsorb VFCs in the sample and obtain more comprehensive data.