## 3 Results and Discussion
### Bacillus subtilis Profiling
\begin{table}
\begin{tabular}{c c c c c c} \hline
**Label** & **Compound** & **CAS** & **Retention Time (min)** & **Retention Index** & **Trend Category** \\ \hline
1 & 1,3-pentadiene & 504-60-9 & 3.282 \(\pm\) 0.015 (n = 6) & 591.2 \(\pm\) 0.2 (n = 6) & 1\({}^{*}\) \\
2 & 2-methylfuran & 534-22-5 & 6.049 \(\pm\) 0.017 (n = 9) & 639.5 \(\pm\) 0.3 (n = 9) & 3 \\
3 & butanal & 123-72-8 & 6.452 \(\pm\) 0.016 (n = 12) & 647.0 \(\pm\) 0.3 (n = 12) & 2\({}^{*}\) \\
4 & 2-butanone & 789-33 & 6.674 \(\pm\) 0.027 (n = 14) & 638.0 \(\pm\) 0.5 (n = 14) & 2\({}^{*}\) \\
5 & trichloromethane & 67-66-3 & 7.495 \(\pm\) 0.008 (n = 27) & 666.7 \(\pm\) 0.2 (n = 27) & 3 \\
6 & 3-methylbutanal & 590-86-3 & 8.986 \(\pm\) 0.005 (n = 18) & 696.3 \(\pm\) 0.1 (n = 18) & 2\({}^{*}\) \\
7 & 2-methylbutanal & 96-17-3 & 9.928 \(\pm\) 0.008 (n = 18) & 702.6 \(\pm\) 0.2 (n = 18) & 2\({}^{*}\) \\
8 & 1-butanol & 716-3 & 10.052 \(\pm\) 0.008 (n = 12) & 718.2 \(\pm\) 0.2 (n = 12) & 1\({}^{*}\) \\
9 & bromochloromethane & 75-27-4 & 11.294 \(\pm\) 0.009 (n = 27) & 744.8 \(\pm\) 0.2 (n = 27) & 3 \\
10 & 1,3-diazine & 289-95-2 & 12.157 \(\pm\) 0.007 (n = 27) & 763.8 \(\pm\) 0.2 (n = 27) & 2\({}^{*}\) \\
11 & dimethyl disulfide & 624-92-0 & 12.387 \(\pm\) 0.005 (n = 30) & 769.0 \(\pm\) 0.1 (n = 30) & 3 \\
12 & 1-methylcyclohexeverine & 591-49-1 & 12.632 \(\pm\) 0.002 (n = 7) & 774.5 \(\pm\) 0.1 (n = 7) & 1\({}^{*}\) \\
13 & 2-methylbutanennitrile & 1896-17-9 & 12.794 \(\pm\) 0.004 (n = 10) & 782.8 \(\pm\) 0.1 (n = 10) & 2\({}^{*}\) \\
14 & toluene & 108-88-3 & 13.105 \(\pm\) 0.006 (n = 29) & 785.3 \(\pm\) 0.1 (n = 29) & 3 \\
15 & 3-methyl-2-pentanone & 209.282-1 & 13.277 \(\pm\) 0.005 (n = 8) & 789.2 \(\pm\) 0.1 (n = 8) & 1 \\
16 & furfural & 98-01-1 & 17.408 \(\pm\) 0.005 (n = 17) & 890.1 \(\pm\) 0.1 (n = 17) & 2\({}^{*}\) \\
17 & 2-heptanone & 110-43-0 & 18.913 \(\pm\) 0.1 (n = 1) & 929.5 (n = 1) & 1\({}^{*}\) \\
18 & 2,5-dimethylpyrazine & 123-32-0 & 19.281 \(\pm\) 0.003 (n = 30) & 939.4 \(\pm\) 0.1 (n = 30) & 2\({}^{*}\) \\
19 &methoxy-phenyl-oxime & & 21.691 \(\pm\) 0.006 (n = 6) & 100.3 \(\pm\) 0.2 (n = 6) & 2\({}^{*}\) \\
20 & benzaldehyde & 100-52-7 & 22.087 \(\pm\) 0.003 (n = 18) & 1017.6 \(\pm\) 0.1 (n = 18) & 2\({}^{*}\) \\
21 & 2-ethyl-5-methylpyrazine & 13360-64-0 & 22.535 \(\pm\) 0.004 (n = 25) & 1030.6 \(\pm\) 0.1 (n = 25) & 2\({}^{*}\) \\
22 & limoneone & 22.969 \(\pm\) 0.004 (n = 15) & 1043.3 \(\pm\) 0.1 (n = 15) & 2\({}^{*}\) \\
23 & dodecane & 112-40-3 & 28.078 \(\pm\) 0.003 (n = 29) & 120.7 \(\pm\) 0.1 (n = 29) & 3 \\
24 & decanal & 112-31-2 & 29.572 \(\pm\) 0.003 (n = 15) & 1251.2 \(\pm\) 0.1 (n = 15) & 2\({}^{*}\) \\
25 & butylated hydroxytoluene & 128-37-0 & 37.804 \(\pm\) 0.004 (n = 12) & 1550.2 \(\pm\) 0.2 (n = 12) & 2\({}^{*}\) \\ \hline \end{tabular}
\end{table} 
Table 1: Compounds of interest identified from solid-phase microextraction (SPME) Arrow sampling of _Backlus subtilis_ over a five-day period. Compound labels refer to labels in Figures 4 and 5. The number of samples used to calculate retention time and retention index for each compound is listed for each value. The longitudinal data for each compound of interest was tested for significance (\(\tau\)) when comparing the level of the compound in the uninoculated control to the bacterial sample over five days. Significance was tested using an unpaired two-tailed Student’s \(t\)-test with \(\alpha=0.05\). When monitoring trends in VOC profile, several analytical priorities exist. First, it is important to use a sampling method that allows a wide range of compounds to be recovered with high efficiency. In this study, this was achieved by implementing the SPME Arrow technique and choosing a fiber type that targeted a wide range of volatiles that were specifically of interest and known to be produced by bacterial metabolism. Second, it is important that the reproducibility of a higher capacity sampling technique remains high priority. In this study, the magnitude of difference in certain VOCs over time and in comparison to blank agar was often very minimal.