Method for the quantification of vanadyl porphyrins in fractions of crude oils by High Performance Liquid Chromatography–Flow Injection–Inductively Coupled Plasma Mass Spectrometry

• HPLC was coupled to FI and ICP-MS for the determination of V linked to porphyrins.
• The mobile phase polarity was optimized to improve peaks resolution and recoveries.
• V in the fractionated oil was present mostly as V-porphyrins.

High performance liquid chromatography hyphenated by flow injection to inductively coupled plasma mass spectrometry (HPLC–FI–ICP-MS) was used to investigate V linked to porphyrins present in fractions of crude oil. First, the crude oil sample was submitted to fractionation by preparative liquid chromatography with UV detection, at the porphyrin Soret band wavelength (400 nm). The obtained porphyrin fractions were then separated in a 250 mm single column, in the HPLC, and eluted with different mobile phases (methanol or methanol:toluene (80:20; v:v)). The quantification of V-porphyrins in the fractions eluted from HPLC was carried out by online measuring the 51V isotope in the ICP-MS, against vanadyl octaethylporphine standard solutions (VO-OEP), prepared in the same solvent as the mobile phase, and injected post-column directly into the plasma. A 20 μg L− 1 Ge in methanol was used as internal standard for minimizing non-spectral interference, such as short-term variations due to injection. The mathematical treatment of the signal based on Fast Fourier Transform smoothing algorithm was employed to improve the precision. The concentrations of V as V-porphyrins were between 2.7 and 11 mg kg− 1 in the fractions, which were close to the total concentration of V in the porphyrin fractions of the studied crude oil.