Creating Greener HPLC Methods as Measured by the AMGS Metric: A Case Study of Improving USP Monograph Methods

Importance of the Topic

High‐performance liquid chromatography remains a cornerstone in pharmaceutical analysis and quality control. Its widespread adoption stems from proven reliability and broad instrument availability. However, traditional HPLC workflows generate significant waste, consume high volumes of organic solvents, and rely on additives that can complicate system maintenance. Implementing greener practices in HPLC not only reduces environmental impact and laboratory costs but also aligns with global sustainability goals.

Study Objectives and Overview

This application note targets the USP monograph method for rivaroxaban and its impurities to:

• Develop an alternative HPLC method guided by green chemistry principles.
• Evaluate both the official USP procedure and the new in-house method using the Analytical Method Greenness Score (AMGS).
• Compare solvent consumption, run times, and greenness metrics to demonstrate practical improvements.

Methodology and Instrumentation

All experiments were performed on a Waters Alliance e2695 HPLC system equipped with a 2489 UV/Vis detector (250 nm) and controlled by Empower 3 software. Separation utilized an XSelect Premier HSS T3 column (4.6 × 100 mm, 3.5 μm) with MaxPeak High Performance Surfaces to minimize non‐specific adsorption. Key parameters for the greener method included:

• Mobile phases: water (A) and bio-based ethanol (B).
• Gradient: 5–95 % B over 16.4 min, hold 2.8 min, re-equilibration to 5 % B in 5.5 min; total cycle time 25 min.
• Flow rate: 1.0 mL/min; column temperature: 30 °C; sample temperature: 10 °C; injection volume: 3 µL.

Main Results and Discussion

The newly developed ethanol–water method achieved baseline separation of rivaroxaban and its four USP-listed impurities in 25 minutes, compared to 37 minutes for the official monograph method (excluding re-equilibration). Solvent usage dropped by approximately 63 % due to elimination of phosphate buffers, ion-pairing agents, methanol, and acetonitrile. AMGS evaluation showed a ~50 % lower total greenness score for the new method, with major gains in the Solvent Energy component. Instrument Energy contributions were also reduced by shorter cycle times. The simpler two‐component mobile phase eliminated long conditioning steps and minimized system contamination risks.

Benefits and Practical Applications

• Reduced environmental footprint through lower solvent volumes and renewable ethanol use.
• Decreased run times and waste disposal costs.
• Elimination of ion-pairing agents simplifies system cleaning and enhances robustness.
• Maintains compliance with USP assay and impurity resolution criteria.

Future Trends and Opportunities

Green analytical chemistry will continue to evolve with:

• Broader adoption of renewable solvents and solvent-less extraction techniques.
• Advanced instrumentation with lower energy demands (e.g., UPLC, microflow systems).
• Integration of real‐time greenness metrics into method development software.
• Regulatory encouragement for ecologically optimized monographs and compendial methods.

Conclusion

By redesigning a USP monograph HPLC method for rivaroxaban around green chemistry principles, significant reductions in solvent use, run time, and waste generation were achieved without compromising analytical performance. AMGS metrics serve as a valuable tool for objectively comparing sustainability across competing methods. Incorporating bio-based solvents and streamlined gradients supports both environmental stewardship and operational efficiency in pharmaceutical quality control laboratories.

References

1. Hicks M, Farrell W, Aurigemma C, Lehmann L, Weisel L, et al. Making the Move Towards Modernized Greener Separations: Introduction of the Analytical Method Greenness Score (AMGS) calculator. Green Chem. 21, 1816–1825 (2019).
2. ACS Green Chemistry Institute Pharmaceutical Roundtable. AMGS online calculator. Accessed February 14, 2024.
3. United States Pharmacopeia. Monograph for Rivaroxaban. USP 43–NF 38, Section 621.
4. Lauber M, Walter TH, Gilar M, DeLano M, Boissel C, et al. Waters Corp. White Paper 720006930 (2020).