Molecular Weight Distributions (MWD) Testing of Excipients

Degradation of excipients can be observed through the rheological behavior studies. Compared with molecular weight averages, MWD provides significantly more information in polymeric excipient analysis, by describing the effect of polymer processing. Therefore, it is crucial to the study of the MWD of pharmaceutical excipient materials as it provides insight into the possible degradation rate of the material and reveals the degraded polymer chains present in the sample. Gel permeation chromatography (GPC, also known as size-exclusion chromatography, SEC), is a well-known technique for understanding the molecular weight distribution of polymers.

Figure 1. Molecular Weight Distribution. (Hong, L.; et al. 2020)

MWD Determination Services

At BOC Sciences, SEC/GPC is a widely used method used to separate molecules based on their hydrodynamic volumes. The principle of the separation is to pass a dilute aqueous or organic polymer solution through a column packed with porous material. In the separation process, smaller molecules gain more volume and thus remain in the column for a longer time, while larger molecules are completely excluded from the pores and are able to pass through the column unhindered.

In the case of hydroxypropyl cellulose

Many pharmaceutical excipients are derived from natural polymers, such as naturally occurring cellulose. Hydroxypropyl cellulose is a commonly used polymeric excipient. A wide MWD, especially on the high molecular weight region, indicates non-uniform processing. The amount of hemicelluloses lost or gained under processing conditions can be determined by particular shoulders in the MWD curve. Therefore, MWD is a useful tool for cellulose quality control as it largely determines the final mechanical properties of the excipient. At BOC Sciences, the MWD of cellulose is usually determined using SEC and molar mass testing systems as well as RI. Moreover, the molecular weight distribution determined by SEC can be further used to analyze the properties of cellulose-based excipients.

In the case of polyolefins

At BOC Sciences, our GPC methodology can be employed for molecular weight distribution determination and chemical composition analysis of many types of polyolefins.

In the case of polyethylene glycol (PEG)

Polyethylene glycols are inert, water-soluble and biodegradable polymers. PEG has a narrow molecular weight distribution and its physical properties are controlled by molecular weight.

Figure 2. Controlling the shape of the molecular weight distribution for rheological properties. (Rosenbloom, S. I.; et al. 2022）

What We Offer?

• The molecular weight distribution is calculated from some key data such as molecular number and average molecular weight (M_n and M_w), polydispersity (PD) and degree of polymerization (DP). Molecular weight is correlated with DP. In the polymeric excipients production, the degree of polymerization may decrease if the process parameters are not ideal.
• MWD symmetry, multimodal distributions, molar mass minimum and maximum, and the molar mass of the most abundant fractions can be accurately evaluated.
• Molecular weight fractions above and below specific values can be determined by cumulative plots.

Advantages of Our Services

• The analytical results and specific properties of the excipients will be modeled using principal component analysis (PCR).
• Our experts use principal component analysis (PCA) and partial-least squares regression (PLS) to investigate the correlation between the variables. The aim is to determine the correlation between sections of MWD and the measured polymeric properties as well as the specific quality properties of the product.
• Light scattering techniques, such as multi-angle laser light scattering (MALLS) measurements are available to provide more accurate MWD data.
• The GPC/SEC technology requires sophisticated data processing, and our experts can handle all the detector signals.