Verifying the Performance of the Integrating Sphere Module on the Thermo Scientific Antaris FT-NIR Analyzer

Significance of the topic

Diffuse reflectance FT-NIR enables rapid, low- or no-preparation analysis of solid and powdered materials across pharmaceutical, chemical and process-analytics sectors. Reliable integrating-sphere based sampling is central to measuring diffuse reflectance from vials or bulk solids with reproducible sensitivity, wavelength accuracy, resolution and long-term stability. Performance verification of an integrating sphere module therefore underpins successful implementation of FT-NIR methods in QA/QC and at-line monitoring.

Objectives and study overview

The study evaluated key performance attributes of the integrating-sphere diffuse reflectance module on the Thermo Scientific Antaris FT-NIR analyzer. Four principal performance areas were assessed: instrument sensitivity (noise/SNR), wavelength accuracy, spectral resolution, and instrument stability/precision during repetitive measurements. Tests used representative solid samples (talc, lactose, talc/lactose mixtures), atmospheric water vapor, and the NIST SRM 1920a reflectance standard. Backgrounds were acquired with an internal computer-controlled gold reference flag to simulate routine automated operation.

Used instrumentation

• Thermo Scientific Antaris FT-NIR analyzer with internal gold-coated integrating sphere module and protective sapphire window
• Automated internal gold reference (diffuse gold flag) for background acquisition
• NIST SRM 1920a reflectance standard (powdered heavy metal oxides in holder)
• Moist air introduced to instrument to acquire water vapor reference
• Thermo Scientific TQ Analyst method development software (classical least squares model)
• Thermo Scientific RESULT software for automated workflow and repeated acquisitions

Methodology

Samples were placed directly on the integrating-sphere window and spectra acquired through the vial bottoms where applicable. Sensitivity (noise) measurements were carried out at 8 cm-1 resolution by collecting a background with the internal gold flag and then a 30-second sample spectrum without moving the reference. Wavelength accuracy was evaluated by comparing measured water-vapor absorption peak positions to HITRAN (1996) reference values; measurements reported at 4 cm-1 resolution. Spectral resolution was assessed by measuring the NIST SRM 1920a at a range of resolutions (2, 4, 8, 16 and 32 cm-1). Long-term precision and instrument stability were tested by creating a CLS calibration for talc content using TQ Analyst, then running an automated RESULT workflow that measured the talc/lactose mixture every 15 minutes over 24 hours while using a single background for the full run to reveal any drift in calculated concentration.

Main results and discussion

• Sensitivity and noise: RMS noise on an 8 cm-1 resolution spectrum was below 10 micro-absorbance units in the 4500 and 6000 cm-1 regions. For diffuse reflectance spectra with strong features (approaching log(1/R) ~ 1), this corresponds to a signal-to-noise ratio on the order of 100,000:1.
• Wavelength accuracy: At 4 cm-1 resolution, measured water-vapor peak positions differed from HITRAN 1996 values by less than 0.3 cm-1 (≈0.1 nm), demonstrating high wavelength fidelity suitable for spectral assignments and chemometric models that rely on accurate band positions.
• Spectral resolution: Spectra of the NIST SRM 1920a collected at resolutions from 2 to 32 cm-1 showed the expected sharpening and detail increase at higher resolution. The authors note the usual trade-off: increased resolution improves spectral specificity but also raises spectral noise.
• Precision and stability: Repetitive monitoring of a ~10% talc-in-lactose mixture using a CLS model and a single background across 24 hours produced 100 consecutive results with mean talc = 9.997% and standard deviation = 0.029%, with negligible systematic drift observed under normal laboratory conditions.
• Practical resolution guidance: For many applications a compromise resolution of 4 or 8 cm-1 offers the best balance between sensitivity and specificity; however, analytes with sharp NIR features (for example talc’s peak near ~7200 cm-1) may benefit from higher resolution.

Benefits and practical applications of the method

• Direct analysis of powders and solids with minimal sample preparation reduces throughput time and risk of contamination.
• High SNR and accurate wavelength calibration support robust quantitative chemometric models and qualitative identification tasks.
• Automated internal reference flag protects the reference, enables background collection without moving samples, and facilitates unattended workflows.
• Demonstrated long-term stability supports routine QA/QC assays and extended automated monitoring (at-line or lab-based) with low drift.
• Suitable for pharmaceutical applications (e.g., talc quantification in formulations), raw-material screening, and process control where reflectance sampling is needed.

Future trends and potential uses

• Integration with advanced chemometrics and machine learning to enhance sensitivity to subtle compositional changes and improve transferability between instruments.
• Expansion to in-line and at-line process analytical technology (PAT) where robust, non-invasive diffuse reflectance measurements enable real-time control.
• Developments in detector technology and sphere coatings to further improve SNR and extend usable spectral range.
• Automation of sample presentation and multi-point sampling adapters to increase representativity for heterogeneous powders and larger solids.
• Standardized procedures and spectral libraries for broader cross-site model transfer and regulated environments.

Conclusion

The Antaris FT-NIR integrating sphere module demonstrates excellent performance for diffuse reflectance measurements: very low noise, high wavelength accuracy, controllable spectral resolution, and outstanding short- and long-term reproducibility. Measured metrics (RMS noise <10 micro-absorbance units at 8 cm-1; wavelength deviations <0.3 cm-1 at 4 cm-1; 24 h repeatability SD = 0.029% for talc content) indicate the module is well suited for routine solid- and powder-analysis in pharmaceutical and industrial settings. The internal gold reference and large accessible sampling area support practical, automated workflows and reduce sample handling artifacts.

References

1. Lowry S., McCarthy B., Verifying the Performance of the Integrating Sphere Module on the Thermo Scientific Antaris FT-NIR Analyzer, Technical Note 51669, Thermo Fisher Scientific.
2. NIST SRM 1920a, Reflectance Standard (powdered heavy metal oxides).
3. HITRAN 1996 molecular spectroscopic database.
4. Thermo Scientific TQ Analyst software documentation.
5. Thermo Scientific RESULT software documentation.