Ultra-short columns for the chromatographic analysis of large molecules

Today, reverse phase liquid chromatography (RPLC) analysis of proteins is almost exclusively performed on conventional columns (100-150 mm) in gradient elution mode. However, it was shown many years ago that large molecules present an on/off retention mechanism, and that only a very short inlet segment of the chromatographic column retains effectively the large molecules. Much shorter columns - like only a few centimetres or even a few millimetres - can therefore be used to efficiently analyse such macromolecules. The aim of this review is to summarise the historical and more recent works related to the use of very short columns for the analysis of model and therapeutic proteins. To this end, we have outlined the theoretical concepts behind the use of short columns, as well as the instrumental limitations and potential applications. Finally, we have shown that these very short columns were also possibly interesting for other chromatographic modes, such as ion exchange chromatography (IEX), hydrophilic interaction chromatography (HILIC) or hydrophobic interaction chromatography (HIC), as analyses in these chromatographic modes are performed in gradient elution mode.