Measurement of Petroleum Fuel Contamination in Water by Solid-Phase Microextraction with Direct Raman Spectroscopic Detection

Abstract

A method is described for determining petroleum fuel contamination in water based on solid-phase microextraction and Raman spectroscopy (SPME/Raman). In this method, contaminants are extracted from aqueous solutions into a solid phase and then detected directly by using spontaneous Raman spectroscopy. The solid phase consists of a small volume (∼ 20 μL) of poly(dimethylsiloxane) that has an optical window in the 830–1600 cm−1 Raman shift region. This region is suitable for determining both aromatic and aliphatic fuel components. Four “real world” fuels—aviation gasoline, unleaded gasoline, jet fuel A, and #1 fuel oil—were used to test this new method. As shown, the SPME/Raman determinations performed in the visible spectral region were not adversely affected from the fluorescence of the marker dyes in these fuels. The linear dynamic ranges for the determinations exceeded the water solubility limits and spanned 1–3 orders of magnitude. The limits of detection with the use of the most sensitive Raman bands in each fuel were in the 8–12 ppm range with the exception of #1 fuel oil (25 ppm), and relative standard deviations typically were 2–10%. Finally, the SPME/Raman method was applied to the determination of total petroleum hydrocarbons in natural water matrices. With the use of hexane and undecane as standards, the results of the determinations compared favorably to the standard methods of purge-and-trap gas chromatography and liquid-liquid extraction followed by infrared detection.