The influence of solvents on the ultraviolet-visible absorption spectra of polycyclic hydrocarbons: Applications in the identification of fuel products by HPLC/UV/MS

Using high-pressure liquid chromatography with ultraviolet-visible (UV) diode-array and mass spectrometric detection, we have analyzed the supercritical pyrolysis products of toluene and of a Fischer-Tropsch synthetic jet fuel. Three polycyclic hydrocarbons, dibenzo[b,ghi]perylene, 8H-dibenzo[a,jk]pyrene, and benzo[pqr]dinaphtho[8,1,2-bcd:2',1',8'-lmn]perylene have been unequivocally identified among the products. First, the mass spectra established the families of the unknown compounds as C26H14, C23H14, and C34H16. Next, the experimental UV absorption spectra of the three products, each obtained in either acetonitrile/dichloromethane or dichloromethane, were compared, respectively, to the published UV spectra of standards of the C26H14 dibenzo[b,ghi]perylene, in ethanol and benzene; the C23H14 8H-dibenzo[a,jk]pyrene, in benzene; and the C34H16 benzo[pqr]dinaphtho[8,1,2-bcd:2',1',8'-lmn]perylene, in 1,2,4-trichlorobenzene. Small differences (of a few nm) between the UV spectra of each product/reference-standard pair were corrected for, based on the refractive index values of the different solvents used. The resulting matching UV spectra established the identities of the three product components as dibenzo[b,ghi]perylene, 8H-dibenzo[a,jk]pyrene, and benzo[pqr]dinaphtho[8,1,2- bcd:2',1',8'-lmn]perylene. It is the fist time that any of these three polycyclic hydrocarbons has been identified as a product of a supercritical reaction environment. It is also the first time that dibenzo[b,ghi]perylene and 8H-dibenzo[a,jk]pyrene have been identified as products of fuel pyrolysis or combustion.