Sorption of volatile C1 to C6 alkanols in plant cuticles

Abstract

The partitioning of a set of 14 primary, secondary and tertiary alkanols with chain-lengths ranging from C1 to C6 in the three-phase system plant cuticle, water and atmosphere was investigated. A static headspace gas chromatographic method was devised for measuring the distribution of the volatile alkanols between the gas, cuticle and aqueous phases, respectively. Measurements were performed in the temperature range from 5–40 °C. The isotherms for the sorption of alkanols in the cuticular polymer matrix (MX) obeyed Henry's law and, at 25 °C, molal MX/air partition coefficients (KMXa) ranging from 454 (methanol) to 33 000 (1-hexanol) were obtained from their slopes. The corresponding experimental air/water partition coefficients (Kaw) varied from 1.94 × 10−4 (methanol) to 8.47 × 10−4 (2-hexanol). MX/water partition coefficients (KMXw) in the range from 0.088 (methanol) to 23 (1-hexanol) were estimated from KMXa, and Kaw. On average, KMXa, was reduced by a factor of two when temperature increased by 10 K. A common reduced isotherm was obtained for all compounds (except methanol) and all temperatures when the concentrations in the MX were plotted versus the ratios of the actual and the saturation vapour pressures. A series of quantitative property/property and structure/property relationships between the parameters for partitioning and simple physico-chemical properties and structural descriptors of the alkanols was established.