Determination of ambient gas-particle partitioning constants of non-polar and polar organic compounds using inverse gas chromatography

Abstract

Gas-particle equilibrium partition coefficients for organic compounds, K i p, are traditionally determined using sample-and-extract methods, in which particles and the surrounding air are simultaneously sampled and concentrations are determined from extracts. Though these techniques are necessary for determining actual ambient concentrations, they have several shortcomings when they are used to gain insight on the sorption properties of ambient particles. Some examples are that (i) the role of relative humidity and temperature are difficult to account for due to fluctuating conditions, (ii) only compounds that are present in ambient air can be studied, and (iii) extracts themselves do not directly indicate if particle-bound compounds are in equilibrium with the air phase or not. An alternative approach that could overcome these shortcomings is inverse gas chromatography (IGC). In this work, we developed an IGC method that uses particle-loaded fiber filters as a stationary phase. The measured retention of analytes injected into the IGC system is a direct measure of the collected particle's sorption behavior. A validation study that used particles with known sorption properties indicates that this approach gives reliable K i p values for a wide variety of compounds. Further, ambient particles from a suburban and urban location were found to be stable over time and to exhibit equilibrium sorption in the IGC, showing that this method is suitable for studying ambient particles. The IGC method presented here is a promising new tool for gaining deeper insights into the gas-particle partitioning behavior of polar and non-polar organic compounds.