Effect of ionic strength on Henry's constants of volatile organic compounds

The effect of ionic strength on Henry's law constants of volatile organic compounds was evaluated in this research using a gas chromatograph-headspace auto sampler system. Concentrations of sodium chloride from 0.1 mol/L to 1 mol/L were used to simulate various ionic strength in water at temperature of 20 degrees C. The salting-out coefficients at 20 degrees C for benzene, toluene, trichloroethylene and tetrachloroethylene were found to be 0.202, 0.240, 0.224 and 0.217 L/mol, respectively. The experimental results also showed that the ionic strength greater than 0.2M can lead to at least a 10% increase in Henry's constants, which in turn favors the partitioning of volatile organic compounds into the air phase. Typical sea water was simulated with 36 parts per thousand sodium chloride and tested at temperatures from 15 degrees C to 45 degrees C. It was found that the van't Hoff's equation predicts the temperature effect very well for sea water. Henry's law constants for the studied volatile organic compounds in the typical sea water are about 30% higher than that in distilled water. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.