Measurements and predictions of hexadecane/air partition coefficients for 387 environmentally relevant compounds.

The logarithm of the hexadecane/air partition coefficient L is a common descriptor for non-specific interaction properties of solutes and is used in poly-parameter linear free energy relationships (pp-LFERs) to predict other partition coefficients. However, the L value data set available for complex and multifunctional substances is rather small. This limits the applicability of the pp-LFER equation. Hence, we experimentally determined L values for 387 complex compounds using GC-retention time measurements on a non-polar column (SPB™ Octyl). The target substances include environmentally relevant compounds such as pesticides, flame retardants and hormones. We determined L values that span a large range of 4.28-15.92. In addition to these experimental measurements several prediction tools (connectivity indices, SPARC, ABSOLV, COSMOthermX) for the L value were evaluated. The root mean squared errors (rmse) were 1.55 (connectivity indices), 1.28 (SPARC), 0.99 (ABSOLV) and 0.94 (COSMOthermX). The number of outliers (prediction error>3) was 18 (connectivity indices), 12 (SPARC), 2 (ABSOLV) and 0 (COSMOthermX). Based on these results the best prediction accuracy in this evaluation is reached by ABSOLV and COSMOthermX, whose results are comparable.