As Product Group Manager here at Malvern Instruments, my portfolio of responsibilities includes products designed to characterize a wide range of materials and formulations, from complex colloids to natural and synthetic polymers including proteins. These products include Malvern’s Zetasizer family of light scattering systems and the Viscotek size exclusion chromatography (SEC) range.

Also referred to as gel permeation chromatography (GPC), SEC is a form of liquid chromatography used for the separation of macromolecules. It is a useful technique for both protein and polymer science and here at Malvern we are continuing to broaden its application potential, for both scientific and commercial advantage.

Characterization of proteins and polymers
You may have read Mark Pothecary’s recent introductory blog; ‘Sizing up the situation’. Now, I would also like to draw your attention to a recent publication that discusses the basic principles of GPC/SEC and weighs up the advantages of the different detection techniques and the associated detectors required.

Published in Chromatography Techniques, the article; “Weighing the Best GPC/SEC Calibration Strategies: From conventional to universal, GPC/SEC comes in many forms”, describes the measurement of molecular weight and the molecular weight distribution using GPC/SEC with single or multiple detection.

Separation requires calibration to convert molecular weight to molecular size
Separation in the GPC/SEC column takes place according to the size of the molecule – typically a single contiguous distribution for polymers or in discrete peaks relating to a protein’s oligomeric structure. However, users most often want to obtain molecular weight data rather than molecular size.  How you make that conversion from size to weight is key to the accuracy of the data.

As the article explains in more detail, by combining different methods of detection using systems such as the Viscotek TDAmax more direct measurements of molecular weight can be made. Used in conjunction with a concentration detector (RI or UV), a light scattering detector can deliver the absolute molecular weight of any protein or polymer sample injected into the GPC or SEC. A viscometer delivers structural data. And, the inclusion of both RI and UV concentration detectors ensures accurate measurement of more complex samples such as copolymers or protein complexes.

We invite you to make your own informed decision
Pushy is not our style here at Malvern. We expect the science to speak for itself and instead recommend you read the article or visit our theory pages and make up your own mind. I would be happy to discuss any questions or concerns you may have as a result. Please feel free to let me know your opinion by commenting below.