What is Size-exclusion Chromatography – Really?

Upon interrogation, most users define size-exclusion chromatography (SEC) as “the type of chromatography you do when using a size-exclusion column.” Furthermore, retention is SEC is defined as “Big analytes come out of the column first, small analytes come out later.” The first definition provides a generally necessary, though not a necessarily sufficient, condition for SEC. The second definition, while useful both for its simplicity and ease of understanding, fails to capture the kinetic and thermodynamic rigor of true SEC retention, i.e., in the absence of non-size-exclusion effects. Nearly a half-century ago, a classic textbook on the subject defined SEC retention as “an equilibrium, entropy-controlled, size-exclusion process.” At the time, this claim was based mostly on circumstantial evidence. Much of the author’s fundamental chromatography work over the past several decades has been devoted to setting all aspects of this last definition on more fundamental footing. These efforts shall be reviewed in the presentation, contextualized withing the framework of the author’s career across industry, academia, and government.