Critical evaluation of predicted and measured gas-liquid partition coefficients in n-hexadecane

Andrew J. Dallas, Peter W. Carr

Research output: Contribution to journalArticlepeer-review

28 Scopus citations

Abstract

Gas-liquid partition coefficients in n-hexadecane determined by packed and capillary column gas chromatography are shown to include contributions from interfacial adsorption. The overall effect of these additional interactions is to increase the value of the gas-liquid partition coefficient and decrease the infinite dilution activity coefficient. Head-space gas chromatography, which is inherently free from the effects of interfacial adsorption, is used to determine the gas-liquid partition coefficient and infinite dilution activity coefficients of 85 nonpolar and polar solutes in n-hexadecane. Through the use of linear solvation energy relationships (LSERs) it is evident that the packed column data contain additional dipolar and hydrogen bond donor and acceptor interactions between solutes and the liquid and solid interfaces. They also indicate that measurements made using capillary columns contain interfacial contributions, but only for extremely strong hydrogen bond acceptor solutes. These additional factors are attributed to interactions between the hydrogen bond donor fused silica silanols and the hydrogen bond acceptor solutes. Since LSERs give a quantitative estimate of the strength of these interactions, we have used them to "correct" previous packed column measurements. This improvement in the existing database of n-hexadecane gas-liquid partition coefficients has significantly aided in our interpretation of the partitioning process. A cavity theory of solutions is used to reevaluate the present understanding of gas-liquid solvation in n-hexadecane. It is shown that a previous interpretation which indicates that solvation in n-hexadecane consists primarily of the cavity formation process and dispersive interactions between the solute and n-hexadecane is basically correct; however, it is shown that as a result of the chosen model the quantitative aspects of the theory have been statistically compromised. For the limited range of solutes studied, the free energy of transfer into n-hexadecane is linearly related to the number of methylene groups within a homolog series; however, the free energy of transfer of a methylene group varies between homolog series. On the basis of the cavity theory of solutions interpretation, this dependence of the methylene group increment on the functional group is shown to be in agreement with the solute dipolarity/polarizability varying throughout and between homolog series.

Original languageEnglish (US)
Pages (from-to)4927-4939
Number of pages13
JournalJournal of physical chemistry
Volume98
Issue number18
DOIs
StatePublished - Jan 1 1994

Fingerprint Dive into the research topics of 'Critical evaluation of predicted and measured gas-liquid partition coefficients in n-hexadecane'. Together they form a unique fingerprint.

Cite this