In Japan, taxed
diesel fuel from non-taxed
fuel oil-A is illegally produced by removing
coumarin, which is added as a non-taxed marker. The
coumarin is removed using concentrated
sulfuric acid and this produces a high viscosity and
hazardous material, called "
sulfuric acid pitch", as a by-product. This compound has a detrimental effect on the environment and is hazardous to humans. The actions have been associated with organized crime with the illegally gained taxes becoming financial bases. To discriminate legal and diesel oil from illegal product, the peak area ratio R(SC), the ratio of total
sulfur to
carbon (>C(14)), was used. R(SC) is calculated by the total areas of
sulfur and
carbon (>C(14)) from the gas chromatogram obtained by gas chromatography-atomic emission detection (GC-AED).
Sulfur in legal
diesel fuels is strictly regulated by a maximum limit, which was 50ppm (and is now 10ppm), but in the preparation of illegal diesel oil, in which
coumarin is eliminated,
sulfur cannot be removed. Therefore, the R(SC) of
fuel oil-A and illegal
fuel oil is over 15, whereas those for legal
fuel oil and
diesel fuel are under 2.0. Furthermore, these ratios do not change in weathering experiments. GC-AED was applied to an actual
arson case and was found to be effective for the determination of total
sulfur in trace amounts of accelerants detected in fire debris at the
arson scene, and hence was effective for the characterization of the ignitable liquids used.