An open workflow for identifying environmental microplastics with an expanded aging spectral library.
At present, identifying pristine or conventional microplastics is no longer the primary challenge. Rather, considerable challenges lie in the identification of environmentally aged microplastics and in determining whether weathered plastic particles still fall within the definition of microplastics. Spectroscopic techniques are widely used for microplastic identification in environmental samples. Raman spectroscopy was adopted here because it provides higher spatial resolution and is less affected by water interference than conventional infrared-based characterization techniques.
Most spectral identification workflows compare unknown particles against reference spectra collected from pristine polymers. This approach can work well for standard plastic materials, but its reliability drops when samples come from real environmental matrices, where plastics are often aged, chemically transformed, or weathered.
The aging spectral library was obtained through in-situ Raman monitoring of real-time spectral evolution as representative plastics transformed under combustion or pyrolysis conditions.
These evolving spectra not only enriched the spectral library but also provided a foundation for defining the identification window and establishing the concept of “Microplastic Derivatives”.
In-situ Raman monitoring in the expanded aging library showed that, as plastic spectra evolve, the 2600-3500 cm-1 region preserves key C-H and N-H stretching features more reliably than many conventional fingerprint-region signals, enabling stronger signals, less interference, and more robust identification.
In situ Raman spectroscopy revealed spectra that retained characteristic polymeric C–H stretching vibrations while diverging markedly from pristine reference spectra. These observations led to the introduction of the concept of Microplastic Derivatives: particles that deviate from conventional polymer structures yet retain essential polymeric features.
Oxidation-resistance observations indicate that aged particles can retain persistent plastic characteristics after thermal transformation.
Tensile testing shows mechanical responses consistent with plastic materials, supporting their classification as altered microplastics rather than unrelated particles.
Mass spectrometric evidence confirms characteristic polymer structures, linking thermally altered spectra back to polymer-derived material.
Important: Because Raman spectroscopy is surface-sensitive, Microplastic Derivative should be understood as an operational category rather than a compositionally pure category.
The web workflow mirrors the scientific framework while keeping each decision visible to the user.
Upload a two-column Raman spectrum with wavenumber in cm-1 and intensity.
Select the sample category and aging type to help OpenMNP evaluate method application scope.
Add anchor points to adjust the baseline or skip correction. Matching uses only 2600-3500 cm-1.
The system checks 3200-3500 cm-1 for possible N-H contribution and lets users confirm or override the library route.
The uploaded spectrum is interpolated onto the same grid and matched against the expanded aging library.
OpenMNP reports the result, matching degree, top hits, standard-only comparison, and optional feedback.
Every uploaded spectrum is interpolated onto the same wavenumber grid before matching. Similarity is reported as matching degree, calculated from Pearson correlation and expressed as a percentage.
To make the advantage of the expanded library visible, OpenMNP also reports a standard-only comparison. This shows how the result would look if only conventional pristine-polymer spectra were used.
The in-situ aging library was acquired with a confocal micro-Raman system coupled to a controlled heating stage (CCR1000 catalytic cell reactor, Linkam).
OpenMNP does not hide preprocessing, spectral regions, thresholds, or matching logic. The method is documented in the ES&T publication and supported by open code so that researchers can inspect, reproduce, and improve the workflow.
