Procedure for and results of simultaneous determination of aromatic hydrocarbons and fatty acid methyl esters in diesel fuels by high performance liquid chromatography

The content of aromatic hydrocarbons in diesel fuels is regulated by appropriate standards, and a further reduction in the allowed concentration of these hazardous substances in these fuels is expected. The content of aromatic hydrocarbons in diesel fuels is most often determined using standard methods EN-12916 or ASTM D-6591. The content of polycyclic aromatic hydrocarbons (PAHs) is determined from a single peak obtained using normal phase high-performance liquid chromatography (NP-HPLC), a column of the NH2 type, n-heptane as the eluent, refractive index detector (RID) and backflushing of the eluent. However, the methods mentioned above cannot be applied when the fuel contains fatty acid methyl esters (FAME), which lately has become more common. The content of FAME in diesel oils is determined using mid-IR spectrophotometry based on the absorption of carbonyl group. However, no standard procedure for the determination of classes of aromatic hydrocarbons in diesel fuels containing FAME is yet available. The present work describes such a modification of methods EN-12916/ASTM D-6591 that provides a simultaneous determination of individual groups of aromatic hydrocarbons, total content of polycyclic aromatic hydrocarbons and the FAME content in diesel fuels. The refractive index detector (RID) and n-heptane as the mobile phase are still used, but backflushing of the eluent is applied after the elution of all polycyclic aromatic hydrocarbons. Additionally, ultraviolet diode array detection is used for the exact determination of low contents of polycyclic aromatic hydrocarbons and to confirm the presence of FAME in the analyzed fuel.