## 3 Results
### selTOCSY Results for Evaporated Petrol Samples  
The investigation of different petrol sources evaporated to 25%, 50%, 75% and 90% of their original weight found distinctive couplings to discriminate between the petrol sources based on 2-methyl-2-butene and the mixture of cis- and trans-2-pentene up to 50% evaporation, except for the BP S petrol source which displayed poor recovery for all relevant olefins. It should be noted that 2-methyl-2-butene and the mixture of cis- and trans-2-pentene were the main olefins contributing to the differentiation between petrol sources. The 75% evaporation samples displayed poor peak resolution, changes in peak intensity and low signal-to-noise ratios resulting in spectra which could not be used for individualization and classification of the petrol sources. The 90% evaporated petrol samples exhibited a complete loss of all the alkene signals that could be used to discriminate between the petrol sources. The petrol samples evaporated to 25% and 50% of their original weight were suitable for individualization and discrimination of petrol sources. The use of \({}^{1}\)H selTOCSY dramatically improved the ability to identify the alkenes which subsequently has the potential to link a petrol sample to its source (Table 3). The spectra are shown in Supplementary Materials.  
\begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline  & **Set 1** & **Set 2** & **Set 3** & **Set 4** \\ \hline Petrol Brand & 3-methyl-1-butene & \
\begin{tabular}{l} Mixture of 1-pentene and \\ 3-methyl-1-butene \\ \end{tabular} & 2-methyl-2-butene &
\begin{tabular}{l} Mixture of cis- and \\ trans-2-pentene \\ \end{tabular} \\ \hline BP S & \(\surd\) & X & X & \(\surd\) \\ \hline BP M & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) \\ \hline Jet & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) \\ \hline Texaco & \(\surd\) & \(\surd\) & X & X \\ \hline Esso & \(\surd\) & \(\surd\) & X & X \\ \hline Shell & \(\surd\) & \(\surd\) & X & X \\ \hline \hline \end{tabular}
\end{table}
Table 2: Summary of the alkene compounds present (\(\surd\)) and absent (X) in the petrol brands.  
\begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Distinctive Set of Olefins** & **Aliphatic Couplings** & **Olefinic Couplings** & **Potential to Discriminate** \\ \hline \multirow{4}{*}{1. 3-methyl-1-butene} & loss of -CH\({}_{3}\) methyl groups and CH couplings at 25\% evaporation rate & decrease in relative intensity of CH couplings at 25\% evaporation rate & \multirow{4}{*}{X} \\ \cline{1-1} \cline{4-4}  & loss of -CH\({}_{3}\) methyl groups and CH couplings at 25\% evaporation rate & decrease in relative intensity of CH couplings at 50\% evaporation rate & \\ \hline \multirow{4}{*}{2. mixture of 1-pentene and 3-methyl-1-butene} & loss of all aliphatic couplings at 50\% evaporation rate & decrease in relative intensity for all couplings up to 50\% evaporation rate, poor resolution was observed for 75\% evaporation rate & \\ \cline{1-1} \cline{4-4}  & & & \\ \cline{1-1} \cline{4-4}  & & & \\ \cline{1-1} \cline{4-4}  & & & \\ \cline{1-1} \cline{4-4}  & & & \\ \hline \hline \end{tabular}
\end{table}
Table 3: A summary table of the aliphatic and olefinic couplings of the individual sets of olefins at 25%, 50% and 75% level of evaporation and their potential to be used for discrimination.