Size-exclusion chromatography (SEC), also known as gel-permeation chromatography (GPC) is a well-known and widely used tool for measuring polymer molecular weight.  Multi-detector SEC measurements including refractive index (RI) and light scattering (LS) can measure absolute molecular weight, independent of a molecules shape, structure, chemistry, or conformation.  Polymer concentration is measured by the RI detector alone.  The addition of a viscometer allows the measurement of intrinsic viscosity (IV), which is used to study conformation and branching, and can expose any structural changes that the polymer may undergo.  

Typical analytical SEC measurements can take approximately 25 to 45 minutes and consume 25 – 45 mL of mobile phase.  This is time-consuming and can be expensive if working with organic solvents.  Ultra- performance liquid chromatography (UPLC) systems use novel SEC column technologies with robust, small particles (<2 µm) to achieve better sample resolution using smaller columns.  This increases productivity, while significantly reducing run-time and cost.  An additional benefit of the reduced solvent use is to effectively make UPLC a ‘greener’ technology than traditional analytical SEC.

The combination of multi-detector SEC and UPLC has, up to now, been challenging due to the significance of inter-detector band broadening (or dispersion); however, the latest developments in integrated multi-detector systems allows up to four detectors to be connected to UPLC systems with only a minimal loss of resolution due to band broadening.

In this application note, Malvern Panalytical’s OMNISEC REVEAL multi-detector module was combined with a Waters ACQUITY™ APC™ system to offer the best of both worlds; high resolution-rapid multi-detector SEC characterization of a PLA-PEO-PLA drug delivery polymer.  The molecular properties of a virgin sample were compared with two samples sterilized by radiation.

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