RESUMO
Total petroleum hydrocarbons (TPHs) in soil are determined by on-line dynamic supercritical fluid extraction (SFE) using infrared filter photometry detection. The filter photometer was constructed in the laboratory using a tungsten lamp, an optical notch filter that selects the C-H stretching vibration of the extracted organics, an optical chopper with demodulation electronics, and a PbSe detector. A modified high-pressure fiber optic flow cell was used to couple the SFE system to the photometer. Quantitation of TPHs was accomplished through the construction of calibration curves of integrated absorbance of C-H stretching (over time) versus concentration. Our studies show that the sensitivity of this system is affected by both the optical path length in the high-pressure cell and the SFE fluid flow-rate, and detection limits for TPHs are in the mid part-per-million range. The results of 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 standard Soxhlet extraction-IR methods.
