Quantitative Assessment of Chemical Modifications of Macromolecules through Counterion Measurement

High Resolution Image Download MS PowerPoint Slide Hyaluronic acid (HA) derivatives are widely used to design biomaterials, but quantifying their degree of chemical modification (DoM) remains challenging with traditional analytical techniques. We present a counterion-based approach that determines DoM by measuring the loss of sodium counterions when carboxylate groups of HA are chemically modified. By focusing on the unmodified carboxylate fraction and its associated Na +, this method provides a universal, label-free readout of modifications. We implement the concept with two complementary techniques: thermogravimetric analysis (TGA) to quantify inorganic residue (sodium carbonate) after decomposition, and inductively coupled plasma optical emission spectroscopy (ICP-OES) to measure sodium content in solution. These methods applied to a series of HA derivatives (aldehyde, furan, thiol, and hydrazide-functionalized HA), yielded DoM consistent with nuclear magnetic resonance and ultraviolet-visible (UV-Vis) spectroscopy reference assays. Each method offers distinct advantages: TGA could analyze insoluble or cross-linked samples hands-free with lower user-induced uncertainty, while ICP-OES provides high sensitivity for soluble samples and multielement detection. Using both in parallel allowed cross-validation of results and highlighted the importance of controlling analysis conditions for certain functional groups. Overall, the counterion-counting strategy is simple, modification-agnostic, and broadly applicable, enabling accurate DoM measurements that support the development and quality control of biomaterials.