Fiber optic probes add flexibility to Raman chemical analysis

Importance of the topic

Raman spectroscopy combined with fiber optic probes enables nondestructive, in situ chemical identification through transparent and translucent containers without sample preparation. This capability is vital for applications requiring operator safety, preservation of sample integrity and rapid analysis of hazardous or sealed materials.

Objectives and study overview

This technical note demonstrates the versatility of fiber optic Raman sampling using a Thermo Scientific DXR3 Flex Raman Spectrometer. The study covers sampling through glass bottles and blister packs, analysis of aqueous solutions, identification of inorganic minerals and pigment mapping on artwork.

Methodology and instrumentation used

Spectra were acquired with a DXR3 Flex Raman Spectrometer equipped with a fiber optic probe. Both 532 nm and 785 nm laser excitations were evaluated; 785 nm was selected for optimal balance of signal and reduced fluorescence. Raman spectra of containers or solvent were measured separately and subtracted from total spectra. Component identification was achieved by matching processed spectra against reference libraries.

Main results and discussion

• Sampling through containers: Liquids and solids were analyzed inside clear and brown glass bottles and blister packaging without opening. Subtraction of minor glass or plastic contributions produced flat baselines and distinct Raman peaks.
• Opaque containers: Analysis through a white polyethylene container pigmented with titanium dioxide revealed container Raman features. Subtraction of container spectrum recovered the spectrum of acetaminophen with clear molecular signatures.
• Aqueous solutions: Water exhibits weak Raman scattering. By subtracting the water spectrum from that of an energy drink, peaks from caffeine, L phenylalanine and potassium sorbate were clearly resolved.
• Inorganic materials: Direct Raman analysis identified calcite, hematite and cerussite deposits on geological specimens. Raman sensitivity to crystal symmetry enabled unambiguous phase and polymorph differentiation.
• Artwork analysis: Raman mapping of white and yellow paints on a painting identified rutile titanium dioxide and lead chromate pigments, illustrating nondestructive cultural heritage applications.

Benefits and practical applications

• Minimal or no sample preparation and nondestructive measurements.
• Enhanced safety via remote, sealed container analysis of toxic or high potency compounds.
• Rapid, in situ identification of chemicals, minerals and pigments through packaging or on surfaces.
• Flexibility and portability using fiber optic probes for large or inaccessible samples.

Future trends and potential uses

Advances in probe design, laser sources and portable spectrometers will expand field and process monitoring capabilities. Integration with chemometric and artificial intelligence algorithms will improve spectral subtraction and automated identification. Emerging applications include real-time pharmaceutical quality control, environmental contaminant detection in sealed systems and mobile analysis of cultural heritage artifacts.

Conclusion

Fiber optic Raman spectroscopy with the DXR3 Flex system and 785 nm excitation delivers versatile, nondestructive chemical analysis through containers, in aqueous environments and on complex surfaces. Simple spectral subtraction and library matching support reliable identification across diverse sample types without any preparation.

Reference

• Thermo Fisher Scientific technical note TN54708_E 03/24M 2024 Thermo Scientific DXR3 Flex Raman Spectrometer application examples