Determination of total petroleum hydrocarbons in soil by on-line supercritical fluid extraction infrared spectroscopy using a fiberoptic transmission cell and a simple filter spectrometer

An on-line supercritical fluid extraction-infrared (SFE-IR) instrument is described for determining total petroleum hydrocarbons (TPHs) in soil samples. This instrument is constructed from a commercially-available SFE system and filter IR spectrometer, and an easily-constructed fiber optic IR cell. All SFEs are performed statically (i.e., no fluid flow once the SFE vessel is filled) for 30 min at 80 degrees C and 340 atm. Detection limits for TPH were determined to be ca. 8 ppm for an IR cell with a 1-mm optical path, and are shown to degrade with increasing pathlength. The results from the application of this on-line SFE-IR instrument to the determination of TPHs in real-world samples show good agreement with those obtained from a standard Soxhlet extraction-IR method. Relative standard deviations of the on-line determinations are in the range of 7-10%. (C) 1997 Elsevier Science B.V.