Equilibrium Vapor Cell for Quantitative IR Absorbance Measurements

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Infrared absorbance measurements through a gas flow cell are made with the closed-loop circulation of vapor/air mixtures equilibrated with the use of temperature-regulated aqueous solutions. Constant reproducible vapor pressures of organic solutes are established with the equilibrated aqueous solutions. The water solvent depresses the vapor pressure of the pure organic solutes of methanol, ethanol, isopropanol, acetone, and methyl ethyl ketone (MEK). Knowledge of the solution liquid mole fractions, the pure component vapor pressures, and the Wilson coefficients permits determination of the solute vapor pressures to within 2% accuracy. Reliable aqueous solution preparation requires only the correct weighings of pure constituent materials before mixing to achieve the targeted solute liquid mole fractions. Absorbances are measured for four of the five solutes over a range of seven concentrations and for MEK over four concentrations. These concentrations show the absorbance region of adherence to Beer's law with an experimental precision of approximately ±2% for the solutes studied. Absorptivities that are calculated from the Beer's law slope are compared to the available infrared absorbance data.

Keywords: Equilibrium vapor cell; FT-IR spectrometry; Infrared absorbance; Quantitative infrared analysis

Document Type: Research Article

DOI: http://dx.doi.org/10.1366/0003702963904935

Affiliations: 1: Department of Chemistry, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061-0212 2: U.S. Army, Edgewood Research Development and Engineering Center, Aberdeen Proving Ground, Maryland 21010-5423

Publication date: October 1, 1996

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