Dual-Column Aromatic Ring Class Separation with Improved Universal Detection across Mobile-Phase Gradients via Eluate Dilution

The herein described High Performance Liquid Chromatography (HPLC) platform (termed HPLC-3) combines a complex solvent gradient with two electron acceptor columns to provide aromatic ring class (ARC) separation for heavy oils. The separation yields seven major fractions: saturates, monoaromatics (1 ring), diaromatics (2 rings), triaromatics (3 rings), tetra-aromatics (4 rings), polyaromatics and polars (5+ polars), and aliphatic sulfides. The system utilizes a photodiode array detector (PDA) for online measurements of aromaticity in series with an evaporative light scattering detector (ELSD) to provide improved quantitative mass determination across the entire solvent gradient. A new postcolumn dilution strategy was successfully utilized to compensate for solvent effects on the ELSD signal. The method allows for calibration across the entire HPLC-3 solvent gradient and simultaneously diverts ∼90% of the sample effluent for fraction collection and further characterization. In addition to the major ARC fractions, the retention characteristics of various heteroatomic functional groups were studied to demonstrate the HPLC-3 system’s ability to further separate polar compounds on the basis of hydrogen bonding