Lignin is the second most abundant natural polymer. However, unlike cellulose, the industrial and technical value of lignin remains unexplored due to the difficulty in characterizing the raw material.
Image Credit: William Edge/Shutterstock.com
Efforts to achieve sustainability are driving the discovery of innovative ways to utilize lignin, with growing research focused on its beneficial applications.
A key characteristic of biopolymers, including lignin, is their molar mass distribution. While lignin was initially thought to be a large macromolecule supporting cellulose in cell walls, research has revealed it to be an oligomer composed of multiple monomer units.
Significant advancements in the molar mass characterization of lignin and its derivative, lignosulfonate, have been achieved by integrating the DAWN™ multi-angle light scattering (MALS) instrument with the Eclipse™ field-flow fractionation (FFF) system or size-exclusion chromatography (SEC).
Lignin and lignosulfonate analysis remain among the most challenging applications for SEC-MALS and FFF-MALS. This article highlights how the advanced technical capabilities of the DAWN and Eclipse systems enable more precise characterization.
Standard Characterization Methods for Lignin and Their Challenges
Contemporary routine approaches for molar mass determination are not beneficial for lignin:
Complicating matters, lignin, with its characteristic aromatic functional groups, tends to fluoresce. SEC-MALS using the standard red laser (λ = 660 nm) is not ideal for most lignin samples, as it excites a broad range of fluorescing moieties at this wavelength.
Fluorophore absorption reduces the incident light intensity reaching the cell, while fluorescence generates additional light at the detector. Both effects can interfere with accurate MALS analysis.
DAWN’s Unique Features for Lignin Characterization
The DAWN instrument incorporates three critical technical features for accurately characterizing lignin and other highly fluorescent samples:
- Forward Monitor: The DAWN’s Forward Monitor measures the light intensity passing through the flow cell. If sample absorption occurs, the Forward Monitor detects a decline relative to pure solvent, enabling precise measurement of the actual light intensity at the scattering volume.
- 785 nm Near-Infrared (NIR) Laser Option: This alternative laser wavelength reduces absorption and fluorescence compared to the standard 660 nm wavelength, minimizing interference.
- Fluorescence-Blocking Filters: These filters prevent fluorescent photons from reaching the photodetectors, ensuring accurate scattering measurements.
SEC-MALS provides consistent and precise results as an absolute method—provided that absorption and fluorescence challenges are addressed. As demonstrated below, this can be achieved with the right tools. Additionally, FFF-MALS offers advanced characterization capabilities that greatly simplify the analysis of these complex materials.
Download the application note to explore the data and analysis in detail.
A DAWN MALS detector integrates with standard HPLC systems. Image Credit: Waters | Wyatt Technology
This information has been sourced, reviewed and adapted from materials provided by Waters | Wyatt Technology.
For more information on this source, please visit Waters | Wyatt Technology.