Analysing copolymers

Viscotek, a specialist in gel permeation chromatography (GPC), has launched a new module for its OmniSEC software package for multiple detection analysis in size separation experiments aimed specifically at the measurement of copolymers.

Copolymers, which consist of chains of alternating, different monomers, are increasingly being used in pharmaceutical products as excipients for parenteral products and to extend the half-life of injectable peptide-based drugs.

The OmniSEC Copolymer module extends the functionality of the package, which is claimed to be the market leader in multifunctional GPC/SEC software. Viscotek notes that, because it is able to import and analyse up to six channels of data simultaneously, OmniSEC is able to cope with "even the most demanding copolymer multi-detector analyses."​

The new copolymer module corrects the limitations of analysis using only a single detector. This is achieved by working out the ratio in response from two concentration detectors - such as refractive index or ultraviolet-visible - to determine the copolymer concentration and generate a true concentration profile.

"Sample types that will benefit most from the new software module include synthetic polymers such as styrene-butadiene copolymers, PEGylated proteins and natural copolymers such as protein polysaccharides,"​ according to Viscotek​.

GPC, also known as size exclusion chromatography (SEC), is the preferred technique for characterising polymers. It does not rely on chemical differences to effect the separation but separates polymer molecules on the basis of their size relative to the pores in the packing material. Its primary use is in measuring molecular weight and molecular weight distributions.

One disadvantage of conventional SEC, which uses a concentration detector such as a refractometer, is that it is unable to distinguish between the effects of molecular weight and structural differences on molecular size. Viscotek has improved the information that can be gleaned using SEC by using three detectors - a concentration detector, viscometer and light scattering detector - acting in concert, with each detector providing complimentary but different information.

In a single GPC experiment, Viscotek's Triple Detection Array (TDA) system can provide information on a sample's absolute molecular weight, molecular size, intrinsic viscosity, conformation and structure, including those with very low molecular weights.

A spokesman for the company told In-Pharmatechnologist.com​ that OmniSEC was designed to fulfil two functions. It provides a low-cost means of gaining a hike in data quality for both researchers who are still using single-detector systems, as well as those who have made the investment in multiple detector systems.