Verifying the Performance of the Fiber Optic Reflectance Probe on the Thermo Scientific Antaris FT-NIR Analyzer

Significance of the Topic

Remote fiber-optic sampling with FT-NIR provides major practical advantages for process analysis and quality control: non-destructive, rapid spectra acquisition directly at-line or in-line, reduced sample handling, and the ability to interrogate opaque containers or hard-to-reach sample locations. Verifying the spectral fidelity, noise performance and stability of a fiber-optic reflectance probe versus a laboratory integrating sphere is essential before deploying probe-based methods in regulated environments (pharma, food, chemical manufacturing) or for transferring methods between sampling geometries.

Goals and Overview of the Study

This technical note evaluates the performance of the Thermo Scientific SabIR diffuse reflectance fiber-optic probe when used with the Thermo Scientific Antaris FT-NIR analyzer. The main objectives were to:

• Compare spectral response and noise of the SabIR probe to an integrating sphere on the same Antaris spectrometer;
• Assess wavelength accuracy using reference materials;
• Evaluate sampling precision and stability over time using a quantitative lactose/talc mix;
• Identify practical considerations and limitations for method transfer between sampling geometries.

The evaluations included spectral comparisons with polystyrene and talc reference materials, repeatability testing (100 repeats over 12 hours), and noise/wavelength accuracy assessments at 2 cm-1 resolution.

Methodology and Instrumentation

Instrumentation and configuration used in the study:

• Thermo Scientific Antaris FT-NIR analyzer configured with a CaF2 beamsplitter, a tungsten-halogen source and a high-sensitivity InGaAs detector.
• SabIR fiber-optic diffuse reflectance probe: bifurcated, randomly mixed low-OH fiber bundle in a stainless-steel probe head with an angled sapphire window; half the fibers deliver light, the other half collect reflected light; includes electronic connector supporting remote start-of-scan and indicator lights.
• Integrating sphere accessory used as the laboratory reference sampling geometry for comparison.
• Reference/sample materials: diffuse gold reference for background, polystyrene calibration sample, KTA-1920x reference (talc with heavy metal oxides related to NIST SRM 1920a) and mixtures of lactose and talc for repeatability/quantitation tests.

Key experimental details:

• Spectra acquired at 2 cm-1 resolution to probe resolution effects on analysis.
• Backgrounds were taken with a gold diffuse reference positioned over the sapphire window; spectral noise was calculated from repeated background measurements.
• Quantitative precision tested via classical least squares calibration for percent talc in lactose/talc mixtures with 100 repetitive measurements over 12 hours; a single background was used prior to the repeatability run to check drift.

Main Results and Discussion

Noise and spectral response:

• RMS spectral noise in the 6000 cm-1 region was found to be less than 20 micro-absorbance units for both the SabIR probe and the integrating sphere, indicating comparable detector-limited noise performance between sampling geometries.
• Direct comparison of polystyrene spectra acquired with the SabIR and integrating sphere showed close agreement; spectral subtraction revealed residual artifacts below ±2 milli-absorbance units, implying spectrometer linearity was not the dominant source of differences.

Wavelength accuracy and spectral features:

• High-resolution spectra of talc and the KTA-1920x reference demonstrate good wavelength accuracy for the SabIR probe when used with the Antaris analyzer.

Sampling-related differences and method-transfer caution:

• Although spectra were broadly similar, differences arose from the SabIR probe’s expanding beam and acceptance angle compared with the integrating sphere. These geometry-driven effects produce wavelength-dependent effective pathlength variations in diffuse reflectance, so methods developed on an integrating sphere may not transfer directly to the SabIR without recalibration or compensation.

Precision and stability:

• Repeatability testing of the lactose/talc mixture (100 measurements over 12 hours, uncontrolled ambient temperature, fiber free to move) produced a standard deviation of 0.037 (percent talc), with no observable drift trend over the measurement period. This indicates good temporal stability and robustness of the fiber-optic probe under routine handling.

Benefits and Practical Applications of the Method

Key practical advantages identified:

• Remote, at-line and in-line sampling capability enabling measurements in reactors, process streams, packaging, or sealed containers without sample removal.
• High sensitivity and low noise comparable to an integrating sphere, enabling quantitative and qualitative NIR analyses in production environments.
• Rugged mechanical design (stainless-steel probe head, sapphire window, low-OH fibers) supports routine use and flexibility in probe placement and handling.
• Electronic interface for remote trigger and indicator lights facilitates rapid screening workflows and operator feedback during manual probe use.

Typical application areas:

• Pharmaceutical raw materials screening and blend uniformity checks.
• Food ingredient verification and moisture/composition monitoring.
• Polymers and solids characterization where non-destructive contact measurements are preferred.
• Process Analytical Technology (PAT) implementations where in-situ or at-line monitoring improves process control.

Future Trends and Potential Uses

Anticipated developments and areas for expanded use:

• Improved probe-specific calibrations and chemometric models that explicitly account for geometry-dependent pathlength effects, easing method transfer between integrating spheres and fiber probes.
• Integration of more sensitive or extended-range detectors to expand usable spectral windows (e.g., extended InGaAs) for applications needing longer-wavelength NIR information.
• Multiplexed or distributed fiber-optic networks enabling simultaneous monitoring at multiple process points and remote centralization of spectral data.
• Embedded real-time analytics and automation for closed-loop process control based on probe measurements.
• Enhancements in fiber robustness (bend-insensitive fibers, contamination-resistant windows) and probe sanitation for stricter regulated environments or harsh process conditions.

Conclusion

The SabIR fiber-optic reflectance probe used with the Thermo Scientific Antaris FT-NIR analyzer delivers performance comparable to an integrating sphere in terms of spectral noise and wavelength accuracy, while offering the operational advantages of remote and in-situ sampling. Geometry-dependent spectral differences were observed and necessitate caution when transferring methods developed on an integrating sphere; however, repeatability and temporal stability are adequate for routine quantitative screening and process monitoring. The probe is appropriate for direct spectral acquisition from containers, packages, or process points when properly validated and calibrated for the sampling geometry.

Reference

Lowry S., McCarthy B., Verifying the Performance of the Fiber Optic Reflectance Probe on the Thermo Scientific Antaris FT-NIR Analyzer. Thermo Scientific Technical Note 51670, 2008.