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Quantification of Volatile Organics in Soil Aging Experiments Using Fourier Transform Infrared Spectroscopy

On-line Fourier transform infrared (FT-IR) spectroscopy was applied to monitor the concentration of halogenated volatile organic compounds in a sample-preparation process that simulates long-term, slow accumulation of contaminants in soils (i.e., aging). Artificial aging is conducted by circulating a supercritical fluid solution containing the contaminant(s) of interest through a packed soil column. Mid-infrared spectra of several volatile halocarbons were measured in supercritical Xe and CO2 to evaluate possible interferences from the strong absorption of CO2. Although some of the C–X bands were partially masked in supercritical CO2, all of the compounds studied had distinct spectral features in the region 1400–700 cm−1 and could be monitored in either solvent. Quantitative measurements of halogenated volatile organics in supercritical CO2 were demonstrated with CCl4. Excellent results were obtained over the range 7–280 mM. Representative artificial aging experiments were conducted on two test soils using CCl4 as the contaminant. On-line (FT-IR) estimates of the aged soil concentrations were 1.3–4.4 times higher than off-line concentrations obtained by gas chromatography/mass spectrometry. The discrepancies were primarily ascribed to post-aging losses that occurred during depressurization and subsequent sample handling. FT-IR spectroscopy is shown to be a powerful tool for monitoring soil loading behavior and for developing artificial aging protocols.