Determination of Saturated Vapor Pressures and Heats of Vaporization from Gas Chromatography Retention Data

Abstract

In modelling the transport and fate of environmentally important chemicals, knowledge of physicochemical parameters such as the saturated vapor pressure (p⁰) and heat of vaporization (D_vapH_m) is critically important. In spite of that, direct measurements of the properties for higher-boiling substances at 298.15 K have been limited to a relatively small number of compounds and, due to experimental difficulties in the low-pressure region (p⁰ < 1 kPa), some of these measurements are of doubtful accuracy. Gas chromatography (GC) is an alternative method for measuring p⁰ and D_vapH_m data, offering advantages in terms of speed, size of solute sample, purity and stability requirements. In this article, several equations proposed to relate GC elution characteristics for low-volatility liquid and solid chemicals to their saturated vapor pressures and heats of vaporization are analyzed and compared. The results support the view that capillary GC is capable of providing D_vapH_m and p⁰ data for non-polar and slightly polar compounds with relative errors of about ± 1-2 % (D_vapH_m) and ± 10-15 % (p⁰) if the method and reference standards are properly selected. Then, the errors are either comparable with or lower than those resulting from more cumbersome direct experimental techniques.