Screening of oil sands naphthenic acids by UV-Vis absorption and fluorescence emission spectrophotometry

Abstract

Oil sands extracted naphthenic acids fractions are known to contain impurities with various levels of unsaturation and aromaticity. These constituents contain functional groups that absorb ultraviolet-visible wavelength (UV-Vis) radiation and give intense florescence emission in contrast to the fully saturated alicyclic naphthenic acids. UV-Vis absorption and fluorescence emission spectrophotometry are presented here as inexpensive and quick screening methods that the detection of chromophoric surrogate compounds that serve as an internal standard for the indirect analysis of oil sands naphthenic acids. The method detection limit for the screening techniques was approximately 1 mg/L with an observed linear range of 1–100 mg/L. The precision of measurements was generally within 10% r.s.d. There was generally good agreement (within 20% r.s.d) for isotherm parameters from non-linear fitting of Langmuir, BET and Freundlich models for sorption of Athabasca oil sands naphthenic acid mixtures to activated carbon samples determined by UV-Vis absorption, fluorescence emission spectroscopy, and conventional direct injection electrospray ionization mass spectrometry.

Keywords:

• Naphthenic acids
• UV-Vis absorbance
• fluorescence detection
• oil sands
• mass spectrometry
• electrospray ionization

Acknowledgments

The authors wish to acknowledge the University of Saskatchewan, NSERC, and Environment Canada for financial support of this research. M.H.M. acknowledges Xia Lu for technical assistance with fluorescence measurements.