Interaction-free GPC/SEC: Column Selection
Solutions for interaction-free GPC/SEC
The key to successful GPC/SEC separations is the correct choice of columns and solvent. Interaction-free GPC/SEC requires a balanced system of sample, mobile phase (solvent), and stationary phase (GPC/SEC column material).
PSS Magic Triangle: Balance the polarity
The sample is the determinant factor: the polarity of the sample defines the polarity of the solvent and that of the stationary phase. Since the polarity of the sample can be from very polar (e.g. Poly (acrylic acid) and other polyelectrolytes) to very unpolar (e.g. Poly(styrene)) it is inescapable to have polar (e.g. SUPREMA) and unpolar (e.g. SDV) stationary phases.
For some applications interaction-free chromatography can be achived by adding a salt or co-solvent to the mobile phase. E.g. in aqueous GPC/SEC often phosphate buffer solutions are used to overcome interactions between the column material surface and the sample. Therefore a careful method development is essential for GPC/SEC.
PSS products and services for interaction-free GPC/SEC
PSS offers high performance GPC/SEC columns ideally suited for reliable and trustworthy molar mass determination and macromolecular characterization.
The PSS column concept is to minimize interactions between polymer and stationary phases by providing stationary phases of different polarities.
PSS offers a column application database where customers can search for their applications. All users can find a column material recommendation there, detailed method information (eluent composition, temperature, ...) is available for PSS NetCommunity members. Alternatively the PSS consumables catalog lists column applications with detailed eluent conditions.
For new materials and applications that are not on the web contact us or use our Column Selection or Method Development service.
Theoretical background interaction-free GPC/SEC
Why is it important that GPC/SEC is interaction-free?
GPC (Gel permeation chromatograpy), or SEC (Size exclusion chromatography), is a chromatographic method that relies on the separation according to the size of the polymer in solution. The size determines the elution volume; larger molecules elute first, since they can not penetrate the pores in the column (stationary phase) and therefore spend less time on the separation column.
GPC/SEC allows to determine molar mass averages (e.g. Mn, Mw, PDI) and the molar mass distribution if
- a calibration curve, that describes the relation between the elution volume and the molar mass, is available (e.g. established using a calibration kit or PSS ReadyCals)
- molar mass sensitive detectors (e.g. an on-line MALLS detetor or an on-line viscometer), that measures the molar mass of the eluting fractions on-line is available
For reliable and precise results both methods require a perfect separation according to size only. If any kind or interaction with the column material appears (leading to a shift in the elution volume), both methods fail. In some cases bulk values, like the Mw for light scattering or the intrinsic viscosity for the viscometer, can still be measured. But distribution information and PDI will be wrong.
So the first goal in GPC/SEC, no matter what detection method is used, is to achieve interaction-free chromatography without any kind of interactions between column material (stationary phase) and sample.
Chromatogram of the same protein measured under 2 different conditions:green: Protein on PROTEEMA in water with 0.3M NaCl. Perfect size separation, expected result.
red: Protein on PROTEEMA in water with 0.03M NaCl. Distorted chromatogram, interactions lead to adsorption, wrong peak form, and wrong elution volumes
The results on a column material with the wrong polarity could even be worse, leading e.g. to irreparable column damage.