Exploring the Value of GPC/SEC in Polysaccharide Characterization

This article examines the information that can be generated using the latest GPC/SEC technology, which brings the sensitivity needed to differentiate similar polysaccharide samples, and the complementary application of flow injection polymer analysis (FIPA), which facilitates application of GPC/ SEC in the manufacturing environment.

Examples of polysaccharides, widely used as food additives and in certain medical applications, include derivatives of cellulose and starch, such as hydroxymethyl cellulose and maltodextrin, respectively; dextrans; and a group of materials increasingly referred to as renewable polymers: xanthan gum, hyaluronic acid, alginates and gum arabic. Polysaccharides occur naturally and are produced by extraction from a plant or animal-based feedstock, rather than being synthesized in polymerization reactions. Such feedstocks have inherent variability, making it difficult to ensure consistent product quality. The performance, and in some cases the safety, of polysaccharide-based products depends on their molecular weight (MW), MW distribution and structure. If the MW of the polysaccharide is too high, then the final product may be too brittle and/or firm, while a low MW may result in a far weaklier structured product and other behavioral abnormalities. Furthermore, at low MW, polysaccharides tend to be linear, but as MW increases, so does the likelihood that the molecule will branch. Branching also directly influences performance in a finished product, so controlling both properties is crucial to ensure a safe and efficacious product that behaves as required. Gel permeation/size exclusion chromatography (GPC/SEC) is used routinely to study the MW and structural characteristics of macromolecules and is useful for polysaccharide characterization. This article examines the information that can be generated using the latest GPC/SEC technology, which brings the sensitivity needed to differentiate similar polysaccharide samples, and the complementary application of flow injection polymer analysis (FIPA), which facilitates application of GPC/ SEC in the manufacturing environment.

Importance of polysaccharide characterization

The need to characterize polysaccharides reliably and comprehensively is shared by those manufacturing polysaccharide-based additives and excipients and the formulators that use them. In the food industry, for example, such additives are routinely used as thickeners and gels and are produced by subjecting natural feedstocks to extraction under closely controlled conditions. Pectin, for instance, is produced from fruit, while carrageenan derives from seaweed. Raw feedstocks for these products may be purchased from numerous suppliers; constituted different, naturally occurring species; and resourced from a wide range of geographies. As a result, they contain a variety of polysaccharide populations, or grades, making optimization of the extraction processes an ongoing challenge. Ensuring consistent, well-defined product quality in the face of this variability relies on timely measurement of the MW of the polymer exiting the extraction process, and analysis of polymeric structure. These measurements support the effective manipulation of extraction conditions to properly grade the product to maintain consistent and desirable quality. Formulation requires an understanding of the structure–function relationships that define the impact of an additive on finished product performance. Here, the MW, MW distribution and structure of a specific additive or grade of additive impact functionality—the rheology of a finished gel, for example, gelation times and compatibility between the additive and other formulation ingredients. Formulators therefore rely on characterization data to differentiate the grades of additive that are commercially available in a way that correlates with their performance, and to identify those features of the polymer that are crucial to delivery of formulation targets. Such data supports effective decision-making about additive and supplier choice. This reliance on MW and structural data makes sensitive, informative characterization of polysaccharides valuable to manufacturers and formulators. The ability to reliably detect subtle differences between samples facilitates extraction optimization and consistent product quality and, for formulators, enables knowledge-driven use. Advances in characterization technology therefore have considerable commercial value.

Tailoring GPC/SEC to meet industrial requirements

All polymers have a chain-like structure, and most commercial products contain chains of differing length. The popularity of GPC/SEC as a standard method for polymer analysis stems from its ability to access the property distributions that polymers consequently exhibit, rather than measuring averaged values. A two-step technique, it involves separation of the sample based on hydrodynamic size, using a packed chromatography column, followed by characterization of the eluting fractions with one or more detectors.

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