## 3 Results and Discussion  
Based on the retention time and spectral search analysis, we found four types of chemical compounds that were consistently present in all of the exhaled breath samples of the patient and control groups (Table 2). We used percentage areas of compounds for the analysis in this study. This is because at this stage, our study aimed to screen for those exhaled breath compounds which are responsible for AD. As a result, we did not carry out additional experiments to calibrate the compounds. Based on the compounds, we found the exhaled breath gas sensor for an optimum detection purpose. The analysis on chemical compounds of an independent exhaled breath sample from an AD patient, a PD patient, and a healthy individual, respectively, is shown in Table 1. The analysis of the percentage area of the peaks found that phenol showed no difference between the groups. A previous study [15] reported the presence of elevated alkane and methylated alkanes groups in AD and PD groups. Additionally, benzene, which was found elevated in the AD and PD groups in the previous report, is highly associated with DNA damage. In our study, alkane and benzene groups were also found with higher percentage areas than other compounds, but not with a statistically significant difference between the studied groups. In contrast, we observed a statistically significant difference from Ethyl 3-cyano-2,3-bis (2,5-dimethyl-3-thienylyl)-acrylate, triphenyl phosphate, and 1-phenanthronol. Actemplate had a higher percentage area of the spectrum in patients with AD than those in the PD and control groups. In particular, lower levels of acetamide were observed in the PD group than in \begin{table}
\begin{tabular}{l c c c c} \hline \hline  & **Compound** & **AD** & **PD** & **Control** & \(p\)**-Value** \\ \hline
**Acetamide** & 25.76 \(\pm\) 3.66 & 20.58 \(\pm\) 1.41 & 24.86 \(\pm\) 3.78 & \(\leq\)0.05 \\ \hline
**Phenol** & 60.45 \(\pm\) 3.87 & 59.88 \(\pm\) 2.28 & 60.00 \(\pm\) 6.54 & ns \\ \hline
**Alkanes** & & & & \\
**Pentadecane** & 0.17 \(\pm\) 0.13 & 0.21 \(\pm\) 0.14 & 0.20 \(\pm\) 0.13 & ns \\
**Tetradecane** & & & & \\ \hline
**Siloxanes** & & & & \\
**Cyclopentassiloxane** & 4.58 \(\pm\) 3.05 & 8.38 \(\pm\) 2.31 & 4.89 \(\pm\) 2.33 & \(\leq\)0.05 \\
**Cyclotrisiloxane** & & & & \\ \hline
**1,2-benzenedicarboxylic acid diethyl ester** & 0.46 \(\pm\) 0.46 & 0.09 \(\pm\) 0.04 & 0.32 \(\pm\) 0.38 & ns \\ \hline
**Ethyl 3-cyano-2,3-bis** & & & & \\
**(2,5-dimethyl-3-thienylyl)-acrylate** & & & & \\ \hline
**Triphenyl phosphate** & 0.03 \(\pm\) 0.03 & nd & 0.07 \(\pm\) 0.07 & \(\leq\)0.05 \\ \hline
**1-phenanthronol** & 0.04 \(\pm\) 0.01 & 0.019 \(\pm\) 0.01 & nd & \(\leq\)0.05 \\ \hline \hline \end{tabular} Data presented as mean \(\pm\) standard deviation. The \(p\)-value for variables was computed using one-way analysis of variance (ANOVA). \(p\leq\) 0.05; ns = not significant; nd = not determined; AD, Alzheimer’s disease; PD, Parkinson’s disease.  
\end{table} 
Table 2: Percentage area of the GC-MS spectrum of chemical compounds found in the exhaled breath samples. the control group. Although the difference was small, it was significant. One study also reported the use of acetamide as a novel acetyl cholinesterase inhibitor, which could potentially be used to treat AD [17]. Perhaps, levels of exhaled acetamide could be associated with the progression of this disease. In addition to those four compounds found consistently in all the exhaled breath samples, there were an additional four types of chemical compounds present in more than 50% of the samples in each group. These included 1,2-benzenedicarboxylic acid diethyl ester, triphenyl phosphate, 1-phenantherol, and ethyl 3-cyano-2,3-bis (2,5,-dimethyl-3-thienyl)-acrylate (Table 2). These compounds were identified and confirmed using retention time and spectral library match. The percentage areas of the spectrum for 1-phenantherol and ethyl 3-cyano-2,3-bis (2,5,-dimethyl-3-thienyl)-acrylate were significantly higher in patients with AD than those in the PD and control groups.