Development of an infrared hollow waveguide as a sensing device for detection of organic compounds in aqueous solutions

In this paper, a new detection method based on an infrared hollow waveguide is developed to detect semivolatile to nonvolatile organic compounds in aqueous solutions. The hollow waveguide is produced by chemical deposition of silver on the inner surface of a polyethylene tube. The surface of the silver layer is further coated with a hydrophobic film to attract organic compounds in aqueous solution. Samples were pumped through this hollow waveguide sampler and organic compounds were attracted onto the hydrophobic film. After removal of the residual water molecules in the hollow waveguide sampler, organic compounds can be sensed by conventional Fourier transform infrared (FT-IR) spectrometry. Theoretical aspects of this type of sampler are also presented. The derived analytical equations for this type of sampler were consistent with experimental data. Under the condition of constant hydrophobic film volume, high linearity (R(2) equal to 0.9993) between the concentration of analyte and the detected signal was obtained for concentrations in the range from 2.5 ppm to 50 ppb. By co-adding 100 scans with 4 cm(-)(1) resolution, the typical detection limit in this type of sensing method can be lower than 10 ppb. Several factors such as sampling flow rate, sampling time, and hydrophobic film volume were also investigated in this work.