What effect does the size of an amino acid on the retention factor?

The retention factor is a value used by chemists performing thin-layer chromatography which indicates the distance a particular compound traveled across a stationary phase in contrast to the solvent. While the size of an amino acid is not the only factor involved, generally, the larger the amino acid, the slower it will travel, ultimately leading to a smaller retention factor.

According to proteomic data analysis, the N-terminus residues highly influence the retention of amino acids due to their role in ion-pairing. Every amino acid has a retention coefficient factor depending on the N-terminus residues it contains. Therefore, the longer the amino acid the higher the likelihood of it having high N-terminus residues and consequent high retention co-efficient.