Directly measuring octanol-air partition ratios using a gas chromatography retention time (GC-RT) method

The octanol-air partition ratio (K_OA) is a fundamental property used for screening chemicals for concern, depending on their potential to bioaccumulate and harm living systems. With millions of chemicals used in commerce, unfortunately, less than 800 compounds currently have experimentally measured K_OA values due to limitations in traditional measurement techniques. We aimed to develop a direct gas chromatography retention time (GC-RT) method using a custom-packed column, with octanol as the stationary phase, for rapidly measuring K_OA. We installed the column into a GC-mass spectrometry system and isothermally measured retention times of 15 volatile organic compounds. We calculated K_OA values at experimental temperatures from the retention times and extrapolated the results to values at 25 °C using the Van't Hoff equation. Our directly measured log K_OA values at 25 °C spanned 3.66 log units (0.820-4.48). Except for alcohols, our measured values agree with literature log K_OA values (root mean square error, RMSE = 0.50). The discrepancy probably arose from differences in how well our method versus the literature methods capture measurement artifacts, specifically, gas-phase adsorption to the octanol phase and hydrogen bonding interactions. This proof-of-concept study demonstrates that our direct GC-RT method is promising for rapidly measuring K_OA to support chemical risk assessment.