A portable vapor cell for passive FT-IR spectrometer evaluation

Abstract

Gravimetrically prepared aqueous binary solutions permit the generation of target vapors of methanol and ammonia in a portable vapor cell. A passive Fourier transform infrared (FT-IR) spectrometer monitors a short pathlength optical cell using a calibrated extended-blackbody background source. The temperature of the blackbody ranges from 5ºC to 50ºC in five degree increments. This temperature range simulates the radiance levels most often encountered for ambient temperature backgrounds in open-air field measurements. The solute liquid mole fractions determine the resultant vapor concentrations. The water component attenuates the target vapor concentration from that of the pure solute component depending on the solute liquid mole fraction. This study demonstrates the utility of a portable vapor cell using a series of binary aqueous solutions per target compound over the Beer's Law range of infrared absorbances. These Beer's Law infrared absorbances and blackbody radiance levels are within the linearity range of the passive FT-IR spectrometer and are representative of open-air field conditions.

A purged-gas containment cell for infrared absorbance measurements

“…The passive FT-IR spectrometer is operated for a period of about seven hours prior to data collection. 1,12 The passive spectrometer is challenged with the Freon 23 at ≈100 ppm-m. Blackbody background temperature ranges from 5ºC to 50ºC in 5ºC increments and 1ºC increments between 15ºC to 25ºC with the PCC at ambient temperature. The single-beam response is shown in Figure 9.…”

“…The PCC windows are composed of low density poly(ethylene) (LPDE) material that has a 0.6 mil thickness. 1 The commercially available thin-LPDE film is used for food packaging and is readily available. The advantages of this window material are threefold: disposable, inexpensive, and refractive index of 1.5.…”