Orbital Raster Scan (ORS™)

Importance of the Topic

Raman spectroscopy provides rapid, non-destructive chemical analysis across diverse fields such as pharmaceuticals, materials science, and forensic testing. Ensuring representative sampling and preserving sample integrity are critical when dealing with heterogeneous or sensitive materials.

Objectives and Study Overview

This application note introduces Metrohm’s patented Orbital Raster Scan (ORS™) technology, which combines a low-power 785 nm laser with a high-etendue spectrograph and rapid beam rastering. The goal is to demonstrate how ORS overcomes limitations of fixed-beam Raman systems in pharmaceutical quality control, polymer identification, and SERS substrate analysis.

Methodology and Instrumentation

ORS employs a tightly focused laser beam that moves in a circular orbit over a sample surface, enabling interrogation of a large area with high spatial resolution and sensitivity. By rastering a 785 nm beam around a 2 000 µm diameter circle, ORS collects averaged spectra from multiple points, reducing local hotspots and sampling bias.

Applied Instrumentation

• MIRA P Advanced – Handheld Raman analyzer with FDA 21 CFR Part 11 compliance, attachment lenses for direct and vial analysis, and Class 3B laser operation.
• MIRA DS Advanced XL – Rugged handheld unit designed for illicit materials, includes a comprehensive Raman library (19 100+ spectra), multiple attachments, and Class 3B operation.
• MISA Advanced – Portable SERS analyzer with Bluetooth/USB connectivity, paper-based P-SERS attachments, nanoparticle solutions, and Class 1 laser safety.

Main Results and Discussion

• Pharmaceutical Sampling: ORS meets European Pharmacopoeia (Ph. Eur.) 2.2.48 requirements by ensuring measurement representativeness through rastered interrogation of tablet surfaces.
• Sample Preservation: Low-power 785 nm excitation (50 mW) in ORS systems minimizes thermal damage compared to 1064 nm fixed-beam lasers (420 mW), preventing sample burning.
• Polymer Identification: A fixed 1064 nm system burned and failed to identify polystyrene and polyphenylene ether, whereas ORS-enabled MIRA XTR DS produced high-quality spectra and achieved HQI 0.91 for both polymers without damage.
• SERS Substrate Analysis: On heterogeneous paper-based P-SERS strips, ORS reduced signal variability (SD 1.4% with raster ON vs 10% OFF), delivering more reproducible trace-level detection of BPE analyte.

Benefits and Practical Applications

ORS technology delivers:

• Representative sampling of heterogeneous and multicomponent specimens.
• High spectral resolution and sensitivity with minimal risk of burning or degradation.
• Consistent, reproducible data for quality control, field screening, and trace analysis.

Future Trends and Potential Uses

Possible developments include:

• Automated surface mapping and chemical imaging using ORS raster patterns.
• Integration with machine learning and chemometric tools for enhanced material classification.
• Further miniaturization of handheld Raman/SERS devices for point-of-care or on-site diagnostics.
• Design of novel SERS substrates optimized for ORS to push detection limits.

Conclusion

Orbital Raster Scan (ORS) effectively addresses the trade-off between sampling representativeness, sensitivity, and sample integrity in Raman analysis. By combining a low-power 785 nm laser, high-etendue spectrograph, and rapid orbital motion, Metrohm’s ORS-enabled analyzers deliver high-quality, reproducible results across pharmaceuticals, polymers, and SERS applications without damaging samples.

Reference

1. European Pharmacopoeia (Ph. Eur.) 10th Edition. European Directorate for the Quality of Medicines (EDQM), 2021.
2. Smith CJ, Stephens JD, Hancock BC, Vahdat AS, Cetinkaya C. Acoustic Assessment of Mean Grain Size in Pharmaceutical Compacts. International Journal of Pharmaceutics. 2011;419(1–2):137–146.
3. Yu WW, White IM. Inkjet Printed Surface Enhanced Raman Spectroscopy Array on Cellulose Paper. Analytical Chemistry. 2010;82(23):9626–9630.