title: Salting-out effect in aqueous NaCl solutions: trends with size and polarity of solute molecules.
abstract: Salting-out in aqueous NaCl solutions is relevant for the environmental behavior of organic contaminants. In this study, Setschenow (or salting-out) coefficients (K(s) [M(-1)]) for 43 diverse neutral compounds in NaCl solutions were measured using a shared headspace passive dosing method and a negligible depletion solid phase microextraction technique. The results were used to calibrate and evaluate estimation models for K(s). The molar volume of the solute correlated only moderately with K(s) (R(2) = 0.49, SD = 0.052). The polyparameter linear free energy relationship (pp-LFER) model that uses five compound descriptors resulted in a more accurate fit to our data (R(2) = 0.83, SD = 0.031). The pp-LFER analysis revealed that Na(+) and Cl(-) in aqueous solutions increase the cavity formation energy cost and the polar interaction energies toward neutral organic solutes. Accordingly, the salting-out effect increases with the size and decreases with the polarity of the solute molecule. COSMO-RS, a quantum mechanics-based fully predictive model, generally overpredicted the experimental K(s), but the predicted values were moderately correlated with the experimental values (R(2) = 0.66, SD = 0.042). Literature data (n = 93) were predicted by the calibrated pp-LFER and COSMO-RS models with root mean squared errors of 0.047 and 0.050, respectively. This study offers prediction models to estimate K(s), allowing implementation of the salting-out effect in contaminant fate models, linkage of various partition coefficients (such as air-water, sediment-water, and extraction phase-water partition coefficients) measured for fresh water and seawater, and estimation of enhancement of extraction efficiency in analytical procedures.
authors.affiliation: Department of Analytical Environmental Chemistry, UFZ - Helmholtz Centre for Environmental Research, Permoserstrasse 15, D-04318 Leipzig, Germany. satoshi.endo@ufz.de
authors.forename: Satoshi
authors.initials: S
authors.lastname: Endo
authors.forename: Andrea
authors.initials: A
authors.lastname: Pfennigsdorff
authors.forename: Kai-Uwe
authors.initials: KU
authors.lastname: Goss
mesh_terms: D005591:Chemical Fractionation; D008401:Gas Chromatography-Mass Spectrometry; D008956:Models, Chemical; D015394:Molecular Structure; D009930:Organic Chemicals / Q000737:chemistry*; D012044:Regression Analysis; D012965:Sodium Chloride / Q000737:chemistry*; D052617:Solid Phase Microextraction; D014867:Water / Q000737:chemistry*
chemical_list: D009930:Organic Chemicals; D014867:Water; D012965:Sodium Chloride