June 15, 2018 (Vol. 38, No. 12)
Thomas Flouquet Application Specialist and Product Manager Novasep
Novasep Designs a Simplified Operation without Compromising Performance
Chromatography is an important and ubiquitous unit operation in downstream bioprocessing. Currently, there are three different ways to pack process chromatography columns:
• Flow packing, which uses constant pressure or flow
After transferring the media slurry into the open column, the piston is quickly mounted in a way that avoids entering air and the column is sealed. Then the mobile phase is pumped either at constant pressure or at constant flow through the column. This causes suspended particles to be packed more quickly and uniformly than gravity settling, reducing the tendency for larger particles to settle first. After the stabilization of the bed height the piston is adjusted accordingly.
• Pack-in-place, which incorporates packing valves
By incorporating multifunctional integrated column valves, pack-in-place employs essentially the same approach as in flow packing but with the added advantage of not having to remove the piston from the column, provided a contained column filling operation is involved.
This method facilitates packing in larger columns and in columns with fixed bed heights. Pack-in-place methods involve pumping the media slurry into the closed column up to a certain pressure rate.
• Dynamic axial packing (DAP), achieved by axially compressing the media slurry
Dynamic axial packing has several advantages over flow pack or pack-in-place procedures. Axially compressing the media slurry accelerates the packing process, reduces size segregation due to gravity settling (and if required, provides a constant compressive force to the whole bed).
The dynamic axial piston movement eliminates the formation of voids or channels in packed beds. This ensures a uniform distribution of the mobile phase across the entire bed. Only one stabilization step is required, compared with the multiple steps employed in flow-packing.
Hardware designs that allow for dynamic axial packing and pack-in-place methods minimize the reliance on operator technique. But until now, the tradeoff was increased hardware costs.
Novasep recently developed the Elemental packing approach on its Prochrom®-Bio DAP columns. Elemental packing combines pack-in-place and dynamic axial packing advantages. It is divided into two steps—introducing the slurry by syringe effect (suction) through a packing valve incorporated into the column flange and then axially compressing the slurry to target bed height.
The Prochrom-Bio column is self-sufficient, i.e., no requirement for extra devices (pumps or packing units), thus allowing for the best packing performance. Indeed, the hydraulically actuated piston can carry out any essential packing and unpacking operations (excluding any heavy/painful handling):
Buffer is introduced into the column by syringe effect (i.e., raising the piston), through both the bottom process line and the packing valve incorporated into column bottom flange. Prochrom-Bio column’s design includes a chamfer, 5 cm above the bottom frit. Once buffer is introduced into the column, lowering the piston below this chamfer enables air removal from the column tube.
Slurry introduction. Similarly, slurry is introduced into the column by syringe effect (Figure 1). The packing valve incorporated into column bottom flange ensures connection between the column and a slurry tank. (Slurry concentration has to be determined prior to be introduced. Robust and reliable methods are available upon request).
Dynamic axial packing is performed by lowering the piston to targeted bed height (Figure 2).
Column unpacking (two available options). Open column unpacking:
Prochrom-Bio columns design allows for a quick and easy column opening by taking out the flange (having previously chased intersticial liquid. Liquid is pushed out from the column by successive piston drops). It is not only fast but also convenient since slurry is recovered at a minimum dilution rate and seals and frits can be inspected, and if required replaced, at a glance.
Closed column unpacking:
In the same way as for packing, piston motion can achieve column unpacking. By connecting a buffer tank to the packing valve and actuating the piston up (to reslurry the media) and then down to expel the reslurried media. The media is recovered with a minimum operation.
Elemental packing/unpacking is a unique and simple method. Watch the full video: bit.ly/2GKCv7q.
Elemental packing produces excellent packing performance and exceptional reproducibility (Figure 3).
The Table summarizes the main column packing requirements and indicates a rating for the different packing methods (green = advantage; orange = not optimal; red = disadvantage).
The principle of Elemental packing is to reduce the tasks and the number of operations and devices to their strict minimum without compromising packing performance. It achieves results in a few minutes on the first attempt.