Large Bubbles Reduce the Surface Sorption Artifact of the Inert Gas Stripping Method

Abstract

Accurate Henry’s law constants between air and water (H) are crucial for understanding a chemical’s environmental behavior. During inert gas stripping (IGS) H is derived from the rate of a chemical’s disappearance from aqueous solution as a result of air bubbling through a water-filled column. While H of many semivolatile organic compounds has been measured by IGS, inconsistent results between different studies have been attributed to chemical adsorption to the bubble surface. This surface adsorption artifact is expected to increase with a chemical’s interface–air partition coefficient (KIA) and decreasing bubble size. Previous work with normal alkanols of variable chain length identified a KIA threshold of approximately 0.001 m, above which IGS is compromised by the surface sorption artifact. In this study, we repeated IGS measurements of H of normal alkanols at different temperatures of 298.15 K, 305.65 K, 323.15 K, and 343.15 K using a modified gas inlet mechanisms that results in the formation of large bubbles (diameter approximately 5.5 mm). The new H values agreed very well with those measured with a head space technique that is much less susceptible to surface adsorption. The method is judged suitable for measuring H of surface active chemicals with KIA values below 0.02 m.