Determination of Temperature-Dependent Henry's Law Constants of Odorous Contaminants and Their Application to Human Perception

摘要

A new method was developed to measure Henry's law constants at varying temperatures and from these data determine enthalpies of reactions for volatilization of aqueous compounds.The method was applied to 2-methylisoborneol (2-MIB),geosmin,and trans-2,cis-6-nonadienal,which are three of the major odorous compounds found in natural and drinking water.The method used static headspace equilibrium in standard odor analysis flasks and SPME-GC/MS.Dimensionless Henry's law constants were determined at 20,25,32,and 39degC in distilled water.Their values ranged from-0.002 to 0.02 and increased with increasing temperature.The study was continued by determining the effects of different concentrations of fulvic acid added to the aqueous media.Decreases of 5-40% in Henry's law constants were observed when fulvic acid was present;however the decrease was not correlated with the fulvic acid concentration.Fulvic acid at any concentration caused a small decrease in constants for geosmin and 2-MIB,yet a more substantial decrease was obtained for nonadienal.Finally,the gas-phase concentrations were predicted using measured Henry's law constants for known aqueous concentrations of 2-MIB,geosmin,and nonadienal at 25 and 45degC.An increase in the gas-phase concentration was not correlated to an increase in human perception as determined by a trained human panel.It is concluded that,after some point,panelists were not able to perceive an increase in the odorant concentration.This has important implications for controlling nuisance odors in the environment.