Quantitative Analysis of Warfarin Tablets Containing Salt-Form Impurities Using Transmission Raman Spectroscopy

Importance of the Topic

Transmission Raman spectroscopy (TRS) enables rapid, nondestructive quantitative analysis of active pharmaceutical ingredients directly in intact tablets. Differentiating and quantifying salt and polymorphic forms of APIs is essential for ensuring content uniformity, stability, and overall product quality.

Objectives and Study Overview

• Evaluate TRS for quantifying Warfarin salt forms (amorphous sodium salt and crystalline clathrate) in whole tablets at low dose (0.5% w/w).
• Assess the ability to distinguish and measure both forms without sample preparation or solvent use.

Instrumentation Used

• Agilent TRS100 Raman quantitative pharmaceutical analysis system
• Beam Enhancer tray to recycle surface-reflected laser light and boost transmission signal
• 830 nm laser at 650 mW power, 20 s acquisition per tablet

Methodology

• Cubic central design of experiments (DoE) with 19 calibration mixtures covering Warfarin concentrations (0.35–0.71% w/w), dye levels, and lactose excipient.
• Production of seven tablets per calibration sample, each scanned in triplicate (399 spectra total).
• Data preprocessing: baseline correction, normalization, first derivative, and mean centering.
• Chemometric modeling using Partial Least Squares (PLS) over 500–850 and 950–1750 cm⁻¹ spectral regions.
• Model validation: R² ≥ 0.99, RMSEC and RMSECV = 0.019% w/w (~4% relative), RMSEP = 0.026% w/w (~5% relative).

Main Results and Discussion

Distinct Raman bands at 680, 818, 1030, 1420, 1460, and 1635 cm⁻¹ provided clear differentiation of sodium salt and clathrate forms. The PLS models achieved high correlation and low prediction errors, even in the presence of a Raman-active dye overlapping in the 1400–1700 cm⁻¹ range. External validation on production batches and placebo samples confirmed robustness.

Benefits and Practical Applications

• Fast, solvent-free, and nondestructive quantification directly on intact dosage forms.
• Enables routine QC of content uniformity and polymorph distribution in pharmaceutical laboratories.
• Reduces reliance on time-consuming chromatographic methods for certain API analyses.

Future Trends and Applications

Future work may extend validation to mixed-form tablets, integrate TRS inline within manufacturing lines, and apply the method to other low-dose APIs and solid-state forms. Enhanced chemometric techniques and advanced optics could further improve sensitivity, specificity, and throughput.

Conclusion

TRS combined with chemometric analysis reliably quantifies Warfarin salt forms at 0.5% w/w in intact tablets. The approach offers a rapid, automated, and eco-friendly alternative for pharmaceutical QC, supporting content uniformity and polymorph assessment.

References

1. Griffen J. A.; Owen A. W.; Matousek P. Quantifying low levels (<0.5% w/w) of warfarin sodium salts in oral solid dose forms using Transmission Raman spectroscopy, J. Pharm. Biomed. Anal. 2018, 155, 276–283.
2. Matousek P. Raman signal enhancement in deep spectroscopy of turbid media. Appl. Spectrosc. 2007, 61, 845–854.