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DNP Enhanced Solid-State NMR Spectroscopy Meets Microplastic – Sample Preparation for Optimal Sensitivity Enhancement
Original title: DNP Enhanced Solid-State NMR Spectroscopy Meets Microplastic – Sample Preparation for Optimal Sensitivity Enhancement
Summary
Scientists developed a faster, more sensitive lab technique to detect chemical changes in microplastics as they break down from sun exposure in the environment. This matters because understanding exactly how microplastics degrade—and what harmful byproducts form—is a key step toward figuring out the risks these particles pose to wildlife and potentially human health. The new method can spot early signs of plastic breakdown in under a minute, much faster than previous techniques, which could speed up research into just how dangerous weathered microplastics really are.
Pollution with microplastic particles is a major environmental challenge of our time. However, little is known about the ecological hazards degraded polymer particles pose. To answer this, a qualification and quantification of the functional groups created by photooxidation of the polymer is necessary. A versatile tool to study this is the bulk method NMR spectroscopy. However, the low sensitivity of this technique makes it difficult to identify and correctly quantify defects in small concentrations. The sensitivity of NMR spectroscopy can be improved via dynamic nuclear polarisation which uses persistent radicals added to the sample. In this work, we investigate four methods to apply these radicals to weathered microplastic samples and discuss the benefits and drawbacks of each method. Our findings show that dissolving the microplastic particles in a solution of AsymPol in trichloroethylene and evaporating the solvent, to create a film yields the best sample for DNP enhanced NMR spectroscopy, as no disturbing solvent peaks remain in the spectrum and the measurement time can by decreased by a factor 35 compared to conventional solid state NMR spectroscopy. With this enhanced sensitivity we were able to measure and identify all defects of a microplastic sample weathered for 3200 h in less than a minute. Furthermore, for the first time, defects are observed in a microplastic sample weathered for only 400 h. This application of DNP enhanced NMR spectroscopy will allow for rapid screening of weathered microplastic particles enabling defect quantification at low concentrations.