Analysis of oil in water at the low ppm level using direct supercritical fluid extraction coupled on-line with infrared spectroscopy

The continued development of direct aqueous SFE instrumentation has enabled the on-line SFE-FTIR analysis of automobile diesel in water at the low ppm level. The integrated system requires minimum sample handling stages with analysis of a 500 ml water sample being completed within 15 min. Diesel-spiked water samples provide a linear response for absorbance values measured at 2932 cm–1 (νasymmetric CH3), through the range 17.2–137.6 ppm. Method accuracy for determining spiked diesel concentrations within this range was greater than 85% with RSD 3–8.6% (n = 4 for each set of spiked calibration standards). The technique allows analyses to be performed with samples containing high levels of particulates and is also suitable for the determination of volatile aromatics and hydrocarbons. The detection limits for benzene and n-decane are 17.6 and 4 ppm, respectively.