Portable Transmission Raman Spectroscopy for At-Line Content Uniformity Testing of Pharmaceutical Tablets

Significance of the Topic

Content uniformity testing is critical in pharmaceutical manufacturing to guarantee each tablet delivers the correct dose of active pharmaceutical ingredient (API). Traditional methods such as HPLC, while accurate, are time‐consuming, destructive, and require extensive sample preparation and consumables. Rapid, noninvasive analytical techniques that can be deployed at‐line offer the potential to streamline quality control and accelerate production.

Objectives and Study Overview

This study demonstrates a proof‐of‐concept for at‐line content uniformity assessment of pharmaceutical tablets using portable transmission Raman spectroscopy. A model tablet formulation containing acetaminophen, mannitol, lactose, microcrystalline cellulose, and magnesium stearate was used to build and validate chemometric models for quantification of acetaminophen and lactose. The goal was to evaluate the performance of the B&W Tek QTRam system coupled with BWIQ and BWAnalyst software for rapid at‐line testing.

Methodology and Instrumentation

Sample Preparation and Formulations:

• Five blends of tablets were prepared, with acetaminophen content ranging from 10 to 18% w/w and lactose from 10.8 to 28.7% w/w; remaining mass comprised mannitol, microcrystalline cellulose, and 1% magnesium stearate.
• Each blend yielded ten round tablets (6 mm diameter, 4.5 mm thickness, ~140 mg) pressed at ~392 kg.

Instrumentation and Measurement Parameters:

• QTRam portable Raman spectrometer equipped with 785 nm laser (max 340 mW) and large‐spot conventional Raman probe.
• Transmission Raman mode: laser illumination on one side, signal collected on the opposite side to sample the full tablet volume.
• Acquisition settings: 100% laser power, 20 s integration, measurements on both tablet faces, three spectra per tablet.

Chemometric Modeling:

• Spectral preprocessing: adaptive iteratively reweighted penalized least squares (air‐PLS) background correction, multiplicative scatter correction (MSC), and first‐derivative Savitzky–Golay filter.
• Region selection for modeling: acetaminophen bands at 1190–1300 and 1530–1700 cm⁻¹; lactose bands at 285–500 and 840–890 cm⁻¹.
• Partial least squares regression (PLS) with four latent factors for acetaminophen and five factors for lactose.
• Calibration set (70% of spectra) and validation set (30%) selected at random, no outliers detected.

Key Findings and Discussion

Model Performance:

• Acetaminophen model: calibration R² = 0.9929, RMSE = 0.233% w/w; validation confirmed high accuracy with standard deviations ≤ 0.17%.
• Lactose model: calibration R² = 0.9915, RMSE = 0.531% w/w; validation deviations also within expected limits.
• BWAnalyst Pass/Fail limits were set at 10–14% for acetaminophen and 18–30% for lactose; only one independent tablet (blend 4) met both criteria.

These results indicate that transmission Raman spectroscopy combined with chemometric modeling can reliably quantify API and excipient levels in intact tablets, offering rapid feedback on content uniformity.

Benefits and Practical Applications

• Non‐destructive, solvent‐free analysis with no sample preparation.
• Rapid measurement (20 s per side) suitable for at‐line or near‐line deployment.
• Full‐volume probing overcomes surface limitations of conventional Raman spectroscopy, including coated tablets.
• Integrated software (BWAnalyst) enables simple Pass/Fail decisions and compliance with regulatory requirements.

Future Trends and Potential Applications

Transmission Raman spectroscopy is poised to expand as a process analytical technology (PAT) tool. Future developments may include:

• Integration into continuous manufacturing lines for real‐time monitoring of tablet quality.
• Extension to multi‐component formulations and low‐dose APIs.
• Improved chemometric algorithms and machine‐learning approaches for enhanced selectivity and robustness.
• Miniaturization and automation for routine quality assurance in production and counterfeit detection.

Conclusion

This case study demonstrates that portable transmission Raman spectroscopy, as embodied by the B&W Tek QTRam system, provides a fast, accurate, and non‐destructive method for at‐line content uniformity testing of pharmaceutical tablets. With minimal sample preparation, high chemical specificity, and regulatory‐compliant software, this approach offers a viable alternative to traditional HPLC and supports more efficient manufacturing workflows.