Identifying polymers with Raman spectroscopy

Despite its precision in analyzing polymers, Raman spectroscopy struggles to accurately identify colored plastics due to fluorescence interference from pigments and additives. Polymer identification results may be less reliable under these conditions.

Utilizing multiple excitation wavelengths, comprehensive reference libraries, and employing advanced techniques all improve the reliability of Raman analysis. Metrohm’s Raman solutions encompass all of these capabilities and provide fast, accurate polymer identification. This Application Note focuses on Metrohm’s advanced XTR® technology which improves identification of substances by eXTRacting the Raman signal from spectra with strong, occluding background fluorescence. Several types of colored polymers are examined, showing the benefits of using 785 nm Raman spectroscopy with the novel XTR fluorescence rejection technique.

All spectra were measured using MIRA XTR, at a wavelength of 785 nm and with Orbital Raster Scan (ORS™), in auto-acquisition mode. Occluding fluorescence initiates XTR algorithms automatically, returning a high-resolution, baselined spectrum of the material.

All samples in this study were common household and office materials, tested through direct contact using the intelligent Universal Attachment (iUA).

Metrohm’s Illicit and General Chemicals Library is a comprehensive spectral database of common materials for accurate identification of mixed samples. Each sample was identified using this library in MIRA Cal software. A range of polymer standards is displayed in Figure 1, illustrating their distinct fingerprints in the Raman spectrum.

Metrohm has unique solutions that overcome the problem of fluorescence while retaining all the benefits of 785 nm interrogation — fast, accurate, nondestructive identification of colored polymers.