Under positive nitrogen pressure a slight excess of either bromonaphthalene

Fig. 2. Direct inlet mass spectrum of (a) 2-[13C]methylnaphthalene, and (b) 9-[13C]methylphenanthrene. The peaks at m/z 143 and 193 correspond to the molecular ion.Figure optionsDownload full-size imageDownload as PowerPoint slide
Fig. 3. 100 MHz 1H NMR spectrum of 9-[13C]methylphenanthrene showing the methyl AS-252424 resonance split by spin–spin coupling to 13C, and signal from residual 12CH3.Figure optionsDownload full-size imageDownload as PowerPoint slide
2.2. Diesel engine tests
The fuels used in the engine tests were: (i) n-hexadecane plus 2000 ppm 2-13[C] methyl-naphthalene and (ii) n-hexadecane plus 2000 ppm 9-13[C] methyl-phenanthrene. The engine was run on pure n-hexadecane before the tests in order to clean the fuel system and engine.
The particulate extracts were analysed as follows. The solvent was removed from the extracts by rotary evaporation and then gentle evaporation under a stream of oxygen-free nitrogen. Extracts were separated into aliphatic, aromatic and polar fractions on a 10 cm long 1 cm diameter column containing 40 μm chromatographic silica by sequential elution with n-pentane, benzene or toluene, and methanol. The solvent was removed from the fractions by gentle evaporation as for the particulate extract. The fractions were weighed and taken up in 250 μL toluene from which 1 μL aliquots were analysed in a Carlo Erba Mega HRGC 5300 capillary gas chromatograph attached via a heated line to a Finnegan MAT 705B ion trap detector. The mass range was set at 50–350 Da with a scan speed of 0.3 s. Both total ion current (TIC) and selective ion monitoring (SIM) chromatograms were recorded. Quantification of the analysis was achieved by use of external standards.