Characterization of fuel samples by on‐line LC‐GC with automatic group‐type separation of hydrocarbons

Characterization of fuels by LC‐GC is possible by use of automatic successive transfer (multiple transfer) of HPLC fractions to a GC via an on‐column interface. This paper describes the instrumentation and the methodology for the HPLC separation of the hydrocarbons (aliphatic and aromatic) into separate groups and the on‐line transfer of these groups to a capillary GC column. Two HPLC methods were used with the same valve configuration: single column (silica) with column back‐flush to detector; and double column (silica and amino‐bonded silica) with multiple fraction transfer and back‐flush. The first method was used for the analysis of total saturated compounds and total aromatic compounds; the second was used for the separation of the one‐, two‐, three‐, and four‐ring aromatic compounds present in diesel fuels. Examples are shown of the characterization of diesel fuels, and the repeatability of the data.