Usage: Guar gum derived from the ground endosperm of the seed of the guar plant is a polysaccharide composed of galactose and mannose units present in a ratio of approximately 2:1. It has many industrial applications which include: textile, paper, pharmaceutical, cosmetics, and nanoparticles industry. In oil fields, guar gum is used to facilitate easy drilling and prevent fluid loss. Guar gum is also used in many food applications as a thickening, emulsifying and stabilizing additive in the production of baked goods and processed cheese among other food products. This polymer has a high molecular weight range of 50,000-8,000,000 determined to suit its desired function in different applications. Triple detection GPC can be used to characterize and confirm the final product.
Manufacturing: There are many different processing techniques that tend to be used depending on the desired properties needed in the final product. The overall process involves roasting of the guar seeds, attrition milling, sieving, and polishing.
Chemical Formula: C17H17ClO6
Figure 1. Molecular structure of Guar Gum
Three guar gum samples were dissolved in water at a concentration of 0.3 percent by volume. Analysis was completed on a Viscotek Triple Detector Array (TDA) 302 equipped with a Refractive Index (RI) detector, Viscometer, Right Angle (90o) Light Scattering (RALS) and Low Angle (7o) Light Scattering (LALS). Separation was performed using three PolyAnalytik AquaGelTM columns (1 x PAA 202 + 1 x PAA 204 + 1 x PAA 206) connected in series. Samples were injected at a volume of 100 µL and eluted through the system at flow rate of 1 mL/min in 0.5 NaNO3. A temperature of 25oC was maintained during separation and detection.
An overlay of the RI signal for three guar gum samples can be seen in Figure 2. A good signal to noise ratio was obtained for each injection. Using the information from all three detectors, as shown in Figure 3 for sample B, molecular weight parameters and size data was derived using triple detection. The data in Table 1 is an average value obtained from 3 injections.
Figure 2. An overlay plot of the RI chromatograms of three guar gum samples
Figure 3. An overlay of the triple-detector response signals of a guar gum sample
Table 1. Molecular weight parameters and size data derived from triple detection using Omni-Sec software.
Triple detection allows for reproducible analysis of the guar gum samples. A standard deviation of less than 5 percent was obtained for all the values reported. Furthermore, the overlaid Mark-Houwink plot of log intrinsic viscosity as a function of molecular weight was constructed as shown in Figure 4, using the intrinsic viscosity determined by the viscometer and the molecular weight determined by the RI and light scattering detectors.
Figure 4. An overlay of the Mark-Houwink plots of three guar-gum samples
Branching information can be obtained from the Mark-Houwink plot; a decrease in the slope on the plot indicates branching is present. The samples are different with respect to branching because they do not completely overlap. Sample C has the largest change in slope suggesting a larger branching ratio. A known linear sample would be needed in order to generate the branching ratio for each sample.
Guar gum has a number of commercial uses in pharmaceuticals, food products, and oil extraction to name a few. Advanced GPC multi-detection method provides a simple procedure to determine molecular weight parameters and degree of branching. Monitoring molecular weight degradation is key because it is related to the performance of the thickener.