Fingerprinting oils in water via their dissolved VOC pattern using mid-infrared sensors

An infrared attenuated total reflection (IR-ATR) method for detecting, differentiating, and quantifying hydrocarbons dissolved in water relevant for oil spills by evaluating the "fingerprint" of the volatile organic compounds (VOCs) associated with individual oil types in the mid-infrared spectral range (i.e., 800-600 cm(-1)) is presented. In this spectral regime, these hydrocarbons provide distinctive absorption features, which may be used to identify specific hydrocarbon patterns that are characteristic for different crude and refined oils. For analyzing the "VOC fingerprint" resulting from various oil samples, aqueous solutions containing the dissolved hydrocarbons from different crude oils (i.e., types "Barrow", "Goodwyn", and "Saladin") and refined oils (i.e., "Petrol" and "Diesel") were analyzed using a ZnSe ATR waveguide as the optical sensing element. To minimize interferences from the surrounding water matrix and for amplifying the VOC signatures by enrichment, a thin layer of poly(ethylene-co-propylene) was coated onto the ATR waveguide surface, thereby enabling the establishment of suitable calibration functions for the quantification of characteristic concentration patterns of the detected VOCs. Multivariate data analysis was then used for a prelininary classification of various oil-types via their VOC patterns.