## 3 Results
### \({}^{1}h\) selfTOCSY Results for Native Petrol Samples  
The \({}^{1}H\) selfTOCSY NMR experiment allowed for more detailed structural and chemical identification of the'source-related' compounds in the olefin region of the spectra. The \({}^{1}H\) selfTOCSY NMR experiments on these alkene signals removed most of the non-alkene-related signals from the spectra, providing additional clarity in the previously heavily overlapped regions of the \({}^{1}H\) NMR spectrum. Therefore, selective \({}^{1}H\) TOCSY was used to elucidate the 'target' compounds of interest not only to identify them but also to use the obtained \({}^{1}H\) selfTOCSY data for building a successful classification model. Figure 4 illustrates spectral examples of the great potential of the \({}^{1}D\) selfTOCSY experiments in revealing the whole spin system of a band-selective chemical shift. The couplings were resolved and can be used to assign the chemical species. Four discriminative sets of olefins were identified: (a) 3-methyl-1-butene by irradiating the signal at 4.64-4.72 ppm, (b) a mixture of 3-methyl-1-butene and 1-pentene by irradiating the signal at 4.73-4.85 ppm, (c) 2-methyl-2-butene by irradiating the signal at 4.95-5.10 ppm and (d) a mixture of cis and trans-2-pentene by irradiating the signal at 5.10-5.35 ppm.  
Figure 3: Representation of the olefin region of the \({}^{1}H\) NMR spectra of neat petrol from different sources: (**i**) British Petroleum Scotland, (**ii**) British Petroleum UK, (**iii**) Jet (Concord), (**iv**) Texaco, (**v**) Esso and (**vi**) Shell.  
Figure 4: _Cont_.  
Figure 4: _Cont._  
Figure 4: \(Cont.\)  
Figure 4: An illustration of the \({}^{1}\)H selfICOSY spectra of the distinctive olefins found in petrol source. (**a**) \({}^{1}\)H selfICOSY spectra displaying the coupling assignment of the irradiated signal at 4.65–4.72 ppm of 3-methyl-1-butene in Jet petrol source. (**b**) \({}^{1}\)H selfICOSY spectra displaying the couplings assignment of the irradiated signal at 4.73–4.85 ppm of the mixture of 3-methyl-1-butene and 1-pentene in Jet petrol source. (**c**) \({}^{1}\)H selfICOSY spectra displaying the couplings assignment of the irradiated signal at 4.95–5.10 ppm of 2-methyl-2-butene in Jet petrol source. (**d**) \({}^{1}\)H selfICOSY spectra displaying the coupling assignment of the irradiated signal at 5.10–5.35 ppm of the mixture of cis- and trans-2-pentene in Jet petrol source.  
It was concluded that petrol sources from BP in Scotland have a unique combination of olefinic compounds that clearly distinguish them from the rest of the petrol sources. The BP M and Jet exhibited similar patterns of the sets of olefins and could not be discriminated on these alone. However, BP M and Jet have the potential to be discriminated from the other three brands based on the couplings of 2-methyl-2-butene. Texaco, Esso and Shell could be potentially discriminated from the other petrol brands based on 2-methyl-2-butene and the mixture of cis- and trans-2-pentene.  
The \({}^{1}\)H selTOCSY method identified the presence/absence of four important sets of olefins representing the minor differences in the signals (Table 2). The summary table shows the combination of different sets of olefins in the petrol brands.