A Method for Determining the Uniquely High Molecular Weight of Chitin Extracted from Raw Shrimp Shells Using Ionic Liquids
Because the very high molecular weight biopolymers extracted from biomass using ionic liquids (ILs) cannot be accurately determined using conventional methodologies (e.g., gel permeation chromatography, intrinsic viscosity measurements, etc.) due to their insolubility in the solvents used for such measurements, we have developed a new method for MW determination based on static light scattering (SLS) in IL solution. The method, based on using SLS measurements to calculate weight average molecular weight (MW) via the Rayleigh equation, was validated by determining the MW for both commercially available (practical grade, PG-) chitin and chitin extracted from raw shrimp shell using 1-ethyl-3-methylimidazolium acetate. We have shown that on average the IL-extracted chitin has a high average MW value, more than three times larger than that for PG-chitin, has a comparatively low polydispersity, and has a degree of acetylation nearly ideal (98(1)% vs. PG-chitin at 82(1)%), thus making the IL-extracted polymer preferable for utilization in materials preparation.