DEAE & SP Spherodex® LS Silica/dextran Composite Ion Exchangers for Liquid Chromatography of Biologicals by Pall Life Sciences Products - Biopharmaceutical Division

DEAE and SP Spherodex® LS ion exchangers are stable composites comprised of two polymers: an inorganic silica matrix which provides a high degree of rigidity to support high flow rates, and an organic dextran component that provides hydrophilicity and biocompatible functional groups.
The resulting interpenetrated polymer network has several advantages such as good chemical stability and bed stability in both aqueous and organic solvents. The sorbent does not shrink or swell with pH or ionic strength, and withstands pressure generated even when exceeding 600 cm/h. The unique network also eliminates non-specific sorption of proteins.

These sorbents were developed specifically for large scale process chromatography of therapeutic proteins and industrial enzymes. Spherodex ion exchange sorbents are presently used in column sizes from 20 to 3,000 L.
 
SP Spherodex LS is supplied in wet form, in an aqueous suspension containing 1 M NaCl and 20% EtOH. DEAE Spherodex LS is supplied in dry form.
The most important properties of these ion exchange sorbents are:

• Stable bed at very high flow rate.
• Stable to pressure (> 50 bar).
• Stable in acidic solutions.
• Highly porous and hydrophilic.
• Low non-specific adsorption.
• No swelling or shrinking, due to aqueous or organic solvents.

Chemical Composition and Structure
Spherodex sorbents are rigid spherical ion exchange matrices comprised of a network of silica and ionizable dextran. The particle size ranges from 100 and 300 µm. The derivatized dextran is uniformly distributed within the pore structure of the silica skeleton (Figure 1). The silica surface is totally covered by dextran, eliminating the activity of active silanol groups. This results in improved stability towards extremes of pH. Additionally, any possible non-specific adsorption on silanols is eliminated.

The dextran polymer carries the classical ionizable groups tightly anchored onto the polymer:

• DEAE (diethylaminoethyl).
• SP (sulfate).
• Additionally, the entire structure is stabilized by chemical cross-linking of the polysaccharide via proprietary patented technology.

Porosity
The structure of the Spherodex network is macroporous, as a result of a specific silica polymerization technology. This open structure offers the following advantages:

• Absence of molecular sieving phenomena.
• Rapid diffusion of macromolecules into the beads (high mass transfer).

Chemical Stability.
Spherodex LS sorbents are insoluble in all solvents. They are also stable to acidic and alkaline solutions, to strong denaturing media, detergents, chaotropic agents, and other organic products.
Classical chemical treatment for sanitization and pyrogen removal can be effected without modifying the ion exchange properties of Spherodex ion exchangers.
Thermal stability.

Spherodex LS ion exchangers are stable over a wide range of temperatures. They can be safely frozen, or autoclaved at 121 ºC. However, it is not advisable to heat DEAE Spherodex repeatedly at 121 ºC because of the progressive degradation of the substituted tertiary amine.
Mechanical stability.

Spherodex ion exchangers are non-compressible and may be submitted to pressures over 50 bar. Pressure thus presents an easy method for increasing the linear column flow rate. This excellent mechanical stability offers additional advantages:

• No variation of the column volume as the ionic strength, pH, or flow rates values are changed.
• Greater flexibility in selecting the working flow rate and changing it during the different phases of the chromatographic cycle.

Protein Sorption Capacity
The protein sorption capacity of Spherodex ion exchangers follows the general rules of the ion exchange mechanism. This sorption capacity depends on a series of factors including pH of the buffer, ionic strength, temperature, nature of the counter ion and intrinsic characteristics of the protein (isoelectric point and molecular weight).

The sorption capacity is primarily affected by the ionic strength of the buffer which controls the ion exchange equilibrium. Typically, an increase in ionic strength leads to a decreased capacity for a given molecule. Temperature increases the rate of exchange and has potential to improve resolution. Differences in counter ion binding constants can provide options to improve resolution.
Changes in pH modify the net charge of the protein and the ionization of the ion exchange functional group as well.