Effect of Salts on the SEC Profiles of Heavy Hydrocarbon Liquids: New Approach with Salts Dissolved in Solvents Used for Planar Chromatography

Abstract

Two related propositions addressing the interpretation of size-exclusion chromatograms of heavy hydrocarbon liquids have been examined. First, that peaks observed at the exclusion (short retention time) limits of size exclusion chromatography (SEC) columns, when using 1-methyl-2-pyrrolidinone (NMP) as eluent, are due to aggregation brought about by sample polarity. Second, that the addition of salts such as LiBr to the NMP eluent dissipates ionic binding forces and causes the disaggregation of polar clusters. The resulting shift to longer elution times (smaller masses) is then interpreted as representing those of the disaggregated sample molecules. However, in earlier work, we observed that the addition of this salt shifted chromatograms to retention times later than the permeation limits of the analytical columns. The salt appeared to have increased surface interactions between the sample and column packing. Thus, the addition of the salt directly to the SEC eluent did not allow distinguishing between an...