# Analysis of _In Vivo_ Plant Volatiles Using Active Sampling and TD-GC\(\times\)GC-TOFMS
## 4 Discussion
### TD Tube vs. SPME  
The total number of peaks observed using both techniques are similar for Mojito mint, whereas for Patriot blueberry, SPME detected more compounds, and active sampling captured more compounds than SPME for Little Napoli tomato. Across all three plants, there was an increase in TPA when using active sampling onto a TD tube. The increase in peak area with TD sampling is evident. This is due to the more exhaustive extraction with a higher absolute recovery of volatiles (inherent to active sampling) for the TD method than for SPME [19; 24]. Additionally, SPME generally works well for moderately volatile \begin{table}
\begin{tabular}{c l c c c c c c c} \hline \hline \multicolumn{1}{c}{**Plant**} & \multicolumn{1}{c}{**Compound**} & \multicolumn{1}{c}{**1\({}_{\text{R}}\) (min)**} & \multicolumn{1}{c}{**2\({}_{\text{R}}\) (s)**} & \multicolumn{1}{c}{**Exp RI**} & \multicolumn{1}{c}{**Library RI**} & \multicolumn{1}{c}{**MS Match**} & \multicolumn{1}{c}{**SPME Peak**} & \multicolumn{1}{c}{**TD Tube**} \\  & & & & & & & & & & \\ \hline \multirow{3}{*}{Mojito Mint} & D-Carvone & 27.83 & 1.82 & 1273 & 1246 & 916 & 1.06 \(\times\) 10\({}^{9}\) & 1.00 \(\times\) 10\({}^{9}\) \\  & Eucalyptus & 21.05 & 1.2 & 1048 & 1032 & 899 & 1.45 \(\times\) 10\({}^{7}\) & 1.40 \(\times\) 10\({}^{8}\) \\  & Limonene \({}^{*}\) & 20.9 & 1.07 & 1044 & 1030 & 917 & 7.47 \(\times\) 10\({}^{7}\) & 2.49 \(\times\) 10\({}^{8}\) \\  & cis-Shydrocarvone & 26.33 & 1.66 & 1219 & 1195 & 878 & 6.69 \(\times\) 10\({}^{7}\) & 6.80 \(\times\) 10\({}^{7}\) \\  & (-)Dibydrocarvyl acetate & 29.92 & 1.31 & 1349 & 1330 & 856 & 1.08 \(\times\) 10\({}^{7}\) & 2.06 \(\times\) 10\({}^{7}\) \\  & \(\gamma\)-Terpinene \({}^{*}\) & 21.12 & 1.11 & 1051 & 1060 & 800 & 5.28 \(\times\) 10\({}^{8}\) & 1.64 \(\times\) 10\({}^{9}\) \\ Little Napoli & 3-Carene \({}^{*}\) & 19.98 & 1.02 & 1016 & 1011 & N/A & 1.06 \(\times\) 10\({}^{8}\) & 6.49 \(\times\) 10\({}^{8}\) \\  & Camphene \({}^{*}\) & 17.64 & 0.94 & 947 & 952 & N/A & N.D. & 5.30 \(\times\) 10\({}^{7}\) \\  & Hexanal & 12.72 & 1.25 & 807 & 801 & 709 & 1.32 \(\times\) 10\({}^{6}\) & 2.06 \(\times\) 10\({}^{7}\) \\  & Humulene \({}^{*}\) & 33.70 & 1.34 & 1494 & 1454 & N/A & 1.83 \(\times\) 10\({}^{7}\) & 1.87 \(\times\) 10\({}^{7}\) \\  & Cyclohexanol & 14.74 & 1.26 & 865 & 880 & 672 & 1.24 \(\times\) 10\({}^{7}\) & 2.20 \(\times\) 10\({}^{7}\) \\ Patriot & 2-Ethyl-2-butenal & 12.65 & 1.33 & 805 & 801 & 670 & 7.16 \(\times\) 10\({}^{6}\) & 1.83 \(\times\) 10\({}^{7}\) \\ Blueberry & 2-Hexen-1-ol (el) (el) & 15.11 & 1.23 & 874 & 868 & 705 & 3.20 \(\times\) 10\({}^{7}\) & 7.96 \(\times\) 10\({}^{6}\) \\  & 4-Hexenyl acetate & 19.95 & 1.22 & 1015 & 1020 & 895 & 2.87 \(\times\) 10\({}^{7}\) & 3.31 \(\times\) 10\({}^{7}\) \\  & Benzaldehyde & 18.63 & 2.13 & 976 & 962 & 607 & 6.11 \(\times\) 10\({}^{5}\) & 1.63 \(\times\) 10\({}^{6}\) \\  & \(\alpha\)-Pinene \({}^{*}\) & 18.48 & 0.96 & 972 & 978 & N/A & N/A & 4.43 \(\times\) 10\({}^{6}\) \\ Sugar Rush & 2-Carene & 19.07 & 1.06 & 989 & 1001 & 730 & N/A & 2.72 \(\times\) 10\({}^{6}\) \\  & \(\alpha\)-Terpinene \({}^{*}\) & 20.09 & 1.12 & 1020 & 1017 & N/A & N/A & 1.49 \(\times\) 10\({}^{6}\) \\ \hline \hline \end{tabular}  
\({}^{1}\)t\({}_{\text{R}}\): first-dimension retention time measured in minutes. \({}^{2}\)t\({}_{\text{R}}\): second-dimension retention time measured in seconds. RI: retention index. Compounds selected based on uniqueness to the respective plant and/or being an abundant compound in the chromatogram. \({}^{*}\) = positively identified with a terpenen standard mix.  
\end{table} 
Table 2: Selected VOCs captured by the _in vivo_ sampling system and their corresponding retention times, retention indices, and peak areas. compounds--those with sufficient volatility to end up in the gas phase, while not being so volatile that they sorb very weakly to the fiber. Figure 1 shows how the TD approach provides better chromatography and analyte recovery in the early portion of the chromatogram.