## 3 Results and Analysis
### Comparison of GC-MS and GC-IMS Results  
Both GC-MS and GC-IMS are excellent instruments for determining volatile compounds, and the research results can better understand the characteristics of the two instruments. The results in Table 2 show that 65 volatile compounds were identified by GC-MS in koumiss samples from four regions. 35 volatile compounds were identified by GC-IMS, of which IMS identified 76 peaks, but 26 peaks were not characterized. Although IMS has a strong sensitivity to the ion drift of volatile compounds without fragmentation and can identify 76 peaks, 26 volatile compounds cannot be confirmed due to incomplete databases. Although GC-IMS is much smaller than GC-MS in the number of substances determined, GC-IMS can conveniently sample and test and quickly obtain results. Among the 50 qualitatively determined volatile compounds, 15 were diploids. When the charged volatile substance is given water and a hydrogen ion, there is a chance that a monomer and two monomers will combine to form a haploid and a diploid [22], making the quantification of volatile compounds by IMS more accurate. Analyzing the types of identified compounds, among the 35 volatile compounds identified by GC-IMS, there are 14 ester compounds, six alcohol compounds, six ketone compounds, and eight aldehyde compounds. Compared with the pattern of identified compounds by GC-MS, GC-IMS is more sensitive to aldehyde and ketone compounds and is more suitable for samples with more aldehyde and ketone compounds. This is consistent with the research results of [PERSON] [23]. In addition, as shown in Figure 3, 13 common volatile compounds were identified by these two types of analysis methods, and a total of 87 volatile compounds were identified, which is much more abundant than the substances determined by a single detection method. Therefore, the combination of GC-IMS and GC-MS can more comprehensively identify and quantify volatile compounds. \begin{table}  
The Characteristic Volatile Compounds of Koumiss from Different Regions Were Analyzed by GC-MS Combined with GC-IMS  
To investigate the aroma characteristics of traditional fermented Kazakh koumiss from different regions, a combined GC-IMS and GC-MS method was used to analyze and identify the volatile compounds and their relative contents in samples from four regions in Xinjiang. As shown in Table 2, a total of 87 volatile flavor substances were detected, including 16 kinds of alcohol compounds (excluding ethanol), 33 kinds of ester compounds, 15 kinds of aldehyde compounds, nine kinds of ketone compounds, three kinds of acid compounds, and one kind each of alkane, phenol, and ether compounds. Compared with the report by [PERSON] [24], more volatile compounds were detected using the combined detection method. As shown in Figure 5, the aroma component types of koumiss samples from the four regions were similar, but the total concentrations of each type varied. The highest content of aroma components was ester compounds, followed by acid compounds, alcohol compounds, and ketone compounds. Ester compounds, acid compounds, and alcohol compounds accounted for a large proportion of the total and were important volatile compounds in koumiss. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**No. **} & \multirow{2}{*}{**Can**} & \multirow{2}{*}{**VOO**} & \multirow{2}{*}{**Identification**} & \multicolumn{4}{c}{**Coantants (ng/kg)**} \\ \cline{4-7}  & & & & & **YL** & **TC** & **ALFlow** & **ALFlow** \\ \hline
214 & 13034-67-6 & ethyl23 hydroxy-methyl reductase & MS & 121.85 \(\pm\) 3.03.0 & 538.80 \(\pm\) 1138.8 & 11312 \(\pm\) 1138.9b & 66.03 \(\pm\) 2.03.0b \\
215 & 424-15-5 &propyl reductase & MS & 66.03 \(\pm\) 17.51. & 60.95 \(\pm\) 57.2 & 8.21 \(\pm\) 102.0b & 9.15 \(\pm\) 6.10b \\
216 & 106-30-9 & Highly hepatoma & MS & 64.60 \(\pm\) 6.88. & 32.76 \(\pm\) 25.4 & 13.30 \(\pm\) 25.6b & 0 \\
217 & 2277-234-8 & 1-Diversity-ice-glycol & MS & 168.18 \(\pm\) 7.78.