In Molecular Sieve Chromatography?

Size-exclusion chromatography (SEC), also known as molecular sieve chromatography, is a chromatographic method in which molecules in solution are separated by their size, and in some cases molecular weight. It is usually applied to large molecules or macromolecular complexes such as proteins and industrial polymers.

Why do large molecules elute first?

Smaller molecules experience a more complex pathway (like a maze) to exit the particle than do larger molecules. Because molecules that have a large size compared to the pore size of the stationary phase have very little entrance into the pores, these larger sized molecules elute first from the column.

What is the molecular sieve effect?

molecular sieve effect (rus. эффект, молекулярно-ситовой) — the effect that includes various availability of the inner space of porous materials for molecules different in size.