Quantitative analysis of modern fuels derived from middle distillates – The impact of diverse compositions on standard methods evaluated by an offline hyphenation of HPLC-refractive index detection with GC×GC-TOFMS.
In this scientific contribution we verified the qualitative and quantitative validity of the DIN EN 12916 or ASTM D6591 based on high performance liquid chromatography with a refractive index detector (HPLC – RID) for the correct determination of aromatic compounds in middle distillates. This was achieved by investigating the influence of the potential insufficient LC separation of aromatic and aliphatic compound classes. The eluent from the HPLC was fractionized according its elution time and these fractions were subsequently analyzed (offline) by comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GC×GC-TOFMS). The methodology was evaluated for common commercial available middle distillates (B0 and B7 Diesel, light heating oil and jet fuel), mixtures of pure diesel fuel with up to 7% hydrogenated vegetable oil (HVO), which serves as an example for a modern advanced premium diesel fuel and different amounts of mono and di-aromatic compounds in HVO as matrix. Compound classes were identified and quantified by applying a data evaluation method which was previously developed in-house  for middle distillates based on GC×GC-TOFMS and Visual Basic Scripting (VBS). Our findings show that the deviations between the results obtained by the GCxGC–MS vs. DIN EN 12916 could be attributed to insufficient separation between compound classes when using the DIN EN 12916 method for current middle distillates. The composition of modern fuels furthermore affects the qualitative as well as the quantitative outcome of industrial established standard methods, and that it is pivotal to revise and develop these analytical techniques in a consequential manner as the composition of fuels and petrochemical products will change and be adapted accordingly to legislative, commercial and environmental changes.