Changes in column length have a direct and linear effect on theoretical plates and analysis time in isocratic separations.  Column length plays a less important role, however, in gradient techniques.  The three chromatograms below illustrate how well packed short HPLC columns yield very similar peptide separations under identical conditions.  For this study, the 2.1mm I.D. HAISIL 300 C18 5µm columns ranged from 250 to 100mm in length.   While solvent and analysis time savings may be minimal, column cost savings can be significant when using as short a column as possible.
 

1. Gly-Tyr
2. Val-Tyr-Val
3. Met Enkephalin
4. Leu Enkephalin
5. Angiotensin II