Evaluation of Direct Fluorescence Spectroscopy for Monitoring Aqueous Petroleum Solutions

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Abstract
The fluorescence of carefully prepared solutions of Ekofisk crude oil in sea water was studied directly in the water phase. Significant fluorescence was observed in the 290–460 nm range for oil solutions well below the concentration level of 10 ppb. On the basis of spectra of single components, the influence of pH on these, and data from gas chromatography/mass spectrometry, it was established that fluorescence at 335 nm (excitation wavelength 230 nm) was dominated by petroleum naphthalenes, while the fluorescence at 300 nm (excitation wavelength 265 nm) could be ascribed to the phenols of the crude oil. For both groups of compounds the intensity of the fluorescence was strongly dependent on the alkylation pattern of the components, making the choice of reference substances in quantitative applications problematic. Quantitative differences in fluorescence itself, could, however, easily be detected with significance, and studies of the preparation and stability of petroleum solutions in sea water are included as examples of application. Properly evaluated, direct fluorescence spectroscopy constitutes a very simple and rapid method for monitoring aqueous petroleum solutions.