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IntroductionBiopolymers are a class of biodegradable and biocompatible polymers used in the medical and pharmaceutical industries. The most common example is PLGA 75:25, a copolymer which can be represented as 75% lactic acid and 25% glycolic acid. The polymers are generally prepared from polymerization of the cylic dimers of the two components. Other biopolymers include PLGA with different ratios of monomoers as well as built on other monomeric units such as caprolactone. While there are currrently no USP or EP monographs for such biopolymers, ASTM has standards for biopolymers such as ASTM F2313 for some PGA and PLGA materials and ASTM F1925 for to PLA polymers. |
Exova Testing Services:Residual catalyst (usually Sn) by ICPMS (validated for several polymers) Residual Heavy Metals by ICPMS as well as USP <231>II Residual solvents by GC and GCMS Identity by FTIR Identity, monomer ratio, and residual monomer by NMR Intrinsic Viscosity |
NMR of PLGAThe most interesting tests we perform on biopolymers is that of identification, monomer ratio, and residual monomer by nuclear magnetic resonance (NMR) spectroscopy. Exova operates a Bruker Avance III 500 MHz system under GMP quality assurance. For a new polymer system, peak assignments in the NMR spectrum generally require a combination of 1H, 13C spectra using DEPT-135, as well as 2D {1H, 13C} HSQC spectra. Exova has already determined peak assignments for lactide, glycolide, and caprolactone polymer systems of various copolymer ratios. Once the peaks are unequivocally assigned, peak integrals can be used to calculate the monomer ratio from both the 1H and 13C spectra. While the 1H spectrum is the most straight forward to obtain, we strongly advise clients to also use the 13C spectrum for confirmation. However to obtain quantitative data from a 13C spectrum, one must use inverse-gated 1H-decoupling and a long interpulse delay which requires much more time to acquire than a simple 1H spectrum. |
The spectra also yield quantitative information about the residual monomer content. The peak assignments for the example spectrum below have been confirmed by detailed analysis of the 1H and 13C NMR spectra as explained above. Note that Charts 2 and 3 are expansions of the Chart 1. The peak assignments are as follows: PLA CH - the polylactide methine proton
quartet split by the PLA methyl protons (PLA CH3),
While this example uses 1H NMR to quantify these components, quantitative 13C NMR was also used to corroborate the 1H results. In our experience, NMR is preferable to gas chromatography for residual monomer. |
1H NMR Spectrum of PLGA
