EQUILIBRIUM VAPOR CELL FOR QUANTITATIVE IR ABSORBENCY MEASUREMENTS

Infrared absorbance measurements through a gas Bow cell are made with the closed-loop circulation of vapor/air mixtures equilibrated with th e use of temperature-regulated aqueous solutions. Constant reproducibl e vapor pressures of organic solutes are established with the equilibr ated aqueous solutions. The water solvent depresses the vapor pressure of the pure organic solutes of methanol, ethanol, isopropanol, aceton e, and methyl ethyl ketone (MEK). knowledge of the solution liquid mol e fractions, the pure component vapor pressures, and the Wilson coeffi cients permits determination of the solute vapor pressures to within 2 % accuracy. Reliable aqueous solution preparation requires only the co rrect weighings of pure constituent materials before mixing to achieve the targeted solute liquid mole fractions. Absorbances are measured f or four of the five solutes over a range of seven concentrations and f or MEK over four concentrations. These concentrations show the absorba nce region of adherence to Beer's law with an experimental precision o f approximately +/-2% for the solutes studied. Absorptivities that are calculated from the Beer's law slope are compared to the available in frared absorbance data.