Although small particle size, nonporous particles for ion exchange such as Agilent’s Bio IEX range offer significant advantages for increased throughput in ion-exchange chromatography, column back pressure can place limitations on the maximum performance that can ultimately be achieved. It is therefore important to understand and appreciate how column pressure can be influenced by factors other than simply the flow rate and column dimensions for these high technology particles.
A grafted hydrophilic polymer layer, containing the ion-exchange functionality, covers the rigid polystyrene (crosslinked with divinylbenzene) core. This helps eliminate nonspecific binding, however the resultant particle is not entirely incompressible or without a slight degree of swell. Consequently it is possible to observe notable changes in column back pressure simply from the buffer composition alone that may not have been noticed when using columns packed with larger particle sizes.
It is important to recognize that, although using a smaller particle size will lead to sharper peaks due to increased column efficiency, column back pressure may begin to become a limiting factor. Furthermore it should also be noted that the choice of buffer salt and the ionic strength of the buffer can also affect the column back pressure as well as separation performance.