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N. Leopold, B. Lendl:
"IR Reflectometric Interference Sensing Approach for Gases";
Poster: Infrared and Raman Discussion Group Christmas Meeting 07, London; 20.12.2007.

IR spectra recorded in reflectance on a ~3 m polymer layer, spin-coated on Si or Ge plates, comprise molecular IR absorption bands and also the interference pattern generated by the polymer film. The polymer layer was exposed to gas analyte, thus enrichment in the polymer film occurred. Analyte specific information is offered by IR absorption and partially by the hydrophobe polymer layer, as it responses predominantly to apolar analytes. Quantitative assessments can be obtained from both, IR absorption and shift of the interference pattern, due to swelling of the polymer layer caused by gas permeation.
The setup for combined IR and reflectometric interference spectroscopy (RIfS) measurements consisted of a homemade Teflon cell with a volume of several cm3 and a 1 mm thick Ge window with a polyisobuthylene (PIB) polymer film spin-coated on the face inside the cell. Exact analyte quantities from a 100 l Hamilton syringe were injected, using a syringe pump, into the air flow. Stainless steel tubings were used to connect the analyte injection point and the gas cell inlet. The IR beam was focused on the polymer layer using an IR microscope objective, that also collected the reflected radiation. Thus, the interference spectrum was generated by the reflected IR radiation at the Ge-polymer and polymer-gas interfaces.
Ethyl acetate was used as analyte and continuously injected in a 70 ml min-1 flow of dry air. Series of measurements with injection flow rates of 1, 2, 3 and 4 l min-1 ethyl acetate were performed (1 l min-1 corresponds to 3300 ppm). Representative difference spectra calculated from IR-RIfS spectra obtained in the presence of dry air and different analyte concentrations are shown in the figure. The shift of the interference pattern is a measure for the analyte concentration. Thus, the time responses of the optical thickness (nd) change of the PIB polymer for the different concentrations of ethyl acetate are also shown in the figure.
The setup was also tested by using other analytes like acetone, cyclohexane and water.

http://publik.tuwien.ac.at/files/pub-tch_8199.pdf

Projektleitung Bernhard Lendl:
Neue chemische Sensoren basierend auf IR Absorptions- und Rflektometrischer Interferenzspektroskopie