Surfactant-enhanced partitioning of nickel and vanadyl deoxophylloerythroetioporphyrins from crude oil into water and their analysis using surface-enhanced resonance Raman spectroscopy

The authors have addressed the identification of molecular fossils of deoxophylloerythroetioporphyrin (DPEP) complexes of vanadium (V) and nickel (Ni) and its partitioning from crude oil into the environment. The analyses described here involve water/surfactant solutions that were in contact with the Boscan crude oil for 1 month. Both VO(DPEP) and NI(DPEP) are identified using resonance Raman (RR) and surface-enhanced resonance Raman (SERR) spectroscopies. Synthetic metalloporphyrins (petroporphyrins) are employed as standards for fingerprinting the naturally occurring crude oil pigments. Supplementary analyses of the Boscan crude oil (source) using inductively coupled plasma (ICP) and ultraviolet-visible (UV-Vis) spectroscopies along with ionic monitoring of the water samples using UV-Vis, ICP, and ion chromatography (IC) were used to assist in establishing their relative abundance and multiple speciation porphyrin forms in the aqueous environment. Results showed that partitioning of V and Ni from the oil phase to the aqueous phase is extremely low and that most of the V and Ni in the aqueous phase is not in ionic form. Although direct partitioning of these metals into the water phase from the oil phase is low, surfactants increase this partitioning of the metalloporphyrin chelates into the water. The results of this study have shown that contamination of drinking water by metals released from crude oils through partitioning is small, and the metals in the aqueous phase are primarily in a complexed form, which further reduces toxicity concerns. Under certain circumstances, it is likely that humic substances, like surfactants, may enhance the partitioning of these complexed metals.