Determination of 1-octanol-air partition coefficient using gaseous diffusion in the air boundary layer

Exact determination of the partition coefficient between 1-octanol and air (K_OA) is very important because it is a key descriptor for describing the thermodynamic partitioning between the air and organic phases. In spite of its importance, the number and quality of experimental K_OA values for hydrophobic organic chemicals are limited because of experimental difficulties. Thus, to measure K_OA values, a high-throughput method was developed that used liquid-phase extraction with 1-octanol drop at the tip of a microsyringe needle. The concentration in the headspace surrounding the 1 μL octanol drop was equilibrated with liquid octanol containing polycyclic aromatic hydrocarbons (PAHs). The change in concentrations of PAHs in the octanol drop was measured to obtain mass transfer rate constants, and these rate constants were then converted into K_OA values using a film diffusion model. Thirteen polycyclic aromatic hydrocarbons with log K_OA between 5 and 12 were chosen for the proof of the principle. Experimental determination of log K_OA was accomplished in 30 h for PAHs with their log K_OA less than 11. The measured log K_OA values were very close to those obtained by various experimental and estimation methods in the literature, suggesting that this new method can provide a fast and easy determination of log K_OA values for many chemicals of environmental interests. In addition, the applicability of the method can be extended to determine Henry's law constant for compounds with low vapor pressure and to estimate gaseous transfer rate of semivolatile compounds for environmental fate modeling.