Purge-and-Trap ATR/IR Spectroscopic Method for the Detection of Semivolatile Aromatic Compounds in Soils

A rapid method for determination of semivolatile compounds in contaminated soil samples was developed by coupling solid-phase microextraction (SPME) with attenuated total reflectance (ATR) Fourier transform infrared (FT-IR) spectroscopy. A trapezoidal internal reflection element was mounted horizontally in a flow cell with the inlet port connected to a temperature-controlled glass extraction chamber. Soil samples were placed inside the glass tube and heated to the desired temperature. Vaporized semivolatile compounds were carried by a stream of nitrogen gas to the ATR/IR flow cell. To increase the trapping efficiency, the ATR crystal was coated with a hydrophobic polyisobutylene polymer that acted as the SPME phase. The method proved to be very sensitive in the detection of semivolatile compounds in soils. The relationship between various parameters affecting chemical quantitation, such as the film thickness, gas flow rate and water contents, was also studied. Three different compounds, 1-chloronaphthalene, nitrobenezene, and 2-chlorotoluene, were used to investigate the feasibility of this method in the analysis of organic compounds in sand and soil. Results indicated a linear relationship between concentration and IR signals can be obtained for the three analytes. The detection limit of this method was in the range of 200−300 ppb.