Direct coupling of normal‐phase HPLC to atmospheric pressure laser ionization FT‐ICR MS for the characterization of crude oil samples

A nitrogen‐rich crude oil sample obtained from Shell was deasphalted by diluting 20 μL of the crude with 100 μL dichloromethane, followed by subsequent addition of 6 ml of n‐hexane. The content was sonicated for 30 min, left standing overnight at room temperature, and filtered to give the maltenes fraction. Chemicals used for sample preparation and solvents for the chromatographic separations are of HPLC grade and supplied by Sigma‐Aldrich (Taufkirchen, Germany).