Infrared Detection of Organics in Artificial Aging Experiments
EMSL Project ID
3412
Abstract
Aging is an important process in which hydrophobic organic compounds become incorporated into a solid matrix during extended contact times (e.g., decades). Contaminants in aged materials exhibit decreased bioavailability and slow release to the environment. The effects of aging on contaminant fate and transport, however, are not well understood and are not accounted for in current numerical models. This is due, in part, to an inability to accurately simulate the aging process on short timescales. Previous research in our laboratory has demonstrated that circulating supercritical carbon dioxide (SC-CO2) can be used to rapidly prepare artificially aged materials that exhibit slow-release behavior. One of the key features of this methodology has been the ability to monitor the progress of the simulated aging process in real time using an in-line ultraviolet (UV) detector. Many contaminants of interest, however, do not absorb in the UV and cannot be monitored using our previous approach. To expand the application of the artificial aging technology to a broader suite of DOE/OFA environmental quality issues, alternative detection approaches are needed.The focus of this project is to evaluate Fourier transform infrared (FTIR) spectroscopy for monitoring artificial aging experiments. FTIR spectrometry has previously been applied as an on-line detector for supercritical fluid chromatography (SFC). A potential problem with this approach, however, is that significant portions of the infrared spectrum are unusable due to absorption by CO2. French and Novotny have advocated the use of supercritical xenon in SFC to avoid this interference problem. Although Xe is relatively expensive, it has convenient critical parameters (Tc = 289.8 K, Pc = 58.0 atm), is optically transparent in the infrared, and is potentially a good solvent for large organic molecules.
Our approach will be to interface an existing FTIR spectrometer to a supercritical fluid loading apparatus using a high-pressure flow cell. The instrument?s noise and baseline characteristics when applied to a circulating supercritical Xe solution will be evaluated. Infrared spectra of supercritical Xe solutions containing selected organic compounds of interest (e.g., carbon tetrachloride, chloroform, tribromofluoromethane, trichloroethene, RDX, and TNT) will be obtained under varying pressure conditions, and practical detection limits will be estimated. For the volatile compounds, we anticipate using 0.1-1.0 mg of analyte per measurement. Likewise, experiments using explosives will be limited to very small quantities (< 0.2 mg). Test soils will be artificially aged with carbon tetrachloride (CCl4) to demonstrate the use of FTIR spectroscopy for monitoring artificial aging experiments. Carbon tetrachloride makes a good test contaminant due to its relevance to Hanford Site contamination problems. Similar loading experiments will also be conducted using supercritical carbon dioxide, and aqueous desorption experiments will be performed to evaluate the slow-release behavior of the aged soils. If soils aged using supercritical Xe behave similarly to soils aged with supercritical CO2, it will be possible to develop loading protocols using Xe (with IR detection) and adapt the protocols to use cheaper CO2 for routine preparation of artificially aged materials.
Project Details
Project type
Exploratory Research
Start Date
2003-04-04
End Date
2005-04-15
Status
Closed
Released Data Link
Team
Principal Investigator
Related Publications
Thompson CJ, RG Riley, JE Amonette, and PL Gassman. 2005. "Quantitation of Organics in Supercritical Fluid Aging Experiments Using FTIR Spectroscopy." American Chemical Society, Washington, DC.