Predicting Sorbent–Air Partition Coefficients for Terpenoids at Multiple Temperatures

Partition coefficients describe the relative concentration of a chemical equilibrated between two phases. In the design of air samplers, the sorbent-air partition coefficient is a critical parameter, as is the ability to extrapolate or predict partitioning at a variety of temperatures. Our specific interest is the partitioning of plant-derived terpenes (hydrocarbons formed from isoprene building blocks) and terpenoids (with oxygen-containing functional groups) in polydimethylsiloxane (PDMS) sorbents. To predict K P D M S / A I Ras a function of temperature for compounds containing carbon, hydrogen, and oxygen, we developed a group contribution model that explicitly incorporates the van't Hoff equation. For the 360 training compounds, predicted K P D M S / A I Rvalues strongly correlate (R 2 > 0.987) with K P D M S / A I Rvalues measured at temperatures from 60 °C to 200 °C. To validate the model with available literature data, we compared predictions for 50 additional C 10 compounds, including 6 terpenes and 22 terpenoids, with K P D M S / A I Rvalues measured at 100 °C and determined an average relative error of 3.1 %. We also compared predictions with K P D M S / A I Rvalues measured at 25 °C. The modeling approach developed here is advantageous for properties with limited experimental values at a single temperature.