A characterization method of skeletal structure for polycyclic aromatic hydrocarbons by molecular ion mass spectrum

A new characterization method of skeletal structure for polycyclic aromatic hydrocarbons (PAHs) has been studied by the soft ionization mass spectrum. The soft ionization, such as field desorption (FD), mass spectrum gives molecular weights of PAHs in coal tars and pitches. PAHs are classified into two types skeletal structure groups. Type-I is the highest H/C group based on kata-type condensation. Type-II is the lowest WC group based on peri-type condensation. The general rational formula of each structures are C(4)n(r+2)H(2)n(r+4) (Type-I) and C(6)n(r)(2)H(6)n(r) (Type-II). In addition, relation between number of aromatic rings (Ra) and molecular weight (Mw), H/C atom ratio and Ra, H/C and Mw are expressed as follows. Ra and Mw, Type-I: Ra=(Mw-28)/50, Type-II: Ra={4Mw-13(8Mw+1)(1/2)+109}/96, H/C and Ra, Type-I: N/C= (Ra+2)/(2Ra+1), Type-II: H/C=6/[{3(4Ra-1)}(1/2)+3]. H/C and Mw, Type-I: H/C=(Mw+72)/(2Mw-6), Type-II: H/C=24/{(8Mw+ 1)(1/2)-1}. Coal tar pitch soluble in toluene and carbon black soluble in acetone are characterized by this method. The average molecular weight of the coal tar pitch soluble in toluene by the field desorption mass spectrum is higher than the carbon black soluble in acetone, But classified molecular ion peaks according to number of aromatic rings,carbon contents of each components of the coal tar pitch soluble in toluene are lower than the carbon black soluble in acetone, This example of the application disclose usefulness of the method for the characterisation of polycyclic aromatic hydrocarbons in coal tars and pitches.