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 deoxo phylloerythroetioporphyrin (DPEP) complexes of vanadium (V) and nickel (Ni) and its partitioning from crude oil into the environment. The analyses des cribed here involve water/surfactant solutions that were in contact with th e Boscan crude oil for 1 month. Both VO(DPEP) and NI(DPEP) are identified u sing resonance Raman (RR) and surface-enhanced resonance Raman (SERR) spect roscopies. Synthetic metalloporphyrins (petroporphyrins) are employed as st andards for fingerprinting the naturally occurring crude oil pigments. Supp lementary analyses of the Boscan crude oil (source) using inductively coupl ed plasma (ICP) and ultraviolet-visible (UV-Vis) spectroscopies along with ionic monitoring of the water samples using UV-Vis, ICP, and ion chromatogr aphy (IC) were used to assist in establishing their relative abundance and multiple speciation porphyrin forms in the aqueous environment. Results sho wed that partitioning of V and Ni from the oil phase to the aqueous phase i s extremely low and that most of the V and Ni in the aqueous phase is not i n ionic form. Although direct partitioning of these metals into the water p hase from the oil phase is low, surfactants increase this partitioning of t he metalloporphyrin chelates into the water. The results of this study have shown that contamination of drinking water by metals released from crude o ils through partitioning is small, and the metals in the aqueous phase are primarily in a complexed form, which further reduces toxicity concerns. Und er certain circumstances, it is likely that humic substances, like surfacta nts, may enhance the partitioning of these complexed metals.