Achieving Method Modernization with the New Liquid Chromatographic Gradient Allowances Provided by USP General Chapter <621> Chromatography and the Alliance™ iS HPLC System

Importance of Topic

The harmonization of USP <621> Chromatography across major pharmacopeias allows modernizing official methods without revalidation, enabling the use of advanced columns and HPLC systems for improved separation efficiency, regulatory compliance, and resource savings.

Study Objectives and Overview

This application note illustrates how to apply the new gradient allowances in USP <621> together with the Waters Alliance iS HPLC System to modernize the antiviral drug abacavir sulfate USP monograph. The primary aims are to adapt column dimensions, flow rates, injection volumes, and gradient profiles while preserving system suitability criteria.

Methodology and Instrumentation

The original monograph method used a 3.9×150 mm, 5 μm L1 C18 column with a defined gradient. Modernization steps included:

• Selecting 4.6×100 mm and 4.6×150 mm columns with 3.5 μm and 5 μm L1 chemistries
• Adjusting flow rate to maintain linear velocity via USP <621> equations
• Scaling injection volume proportionally to column volume
• Timing gradient initiation based on column volume multipliers
• Verifying calculations using Waters online column calculators

No dwell-volume correction was applied due to method specifics.

Used Instrumentation

• Alliance iS HPLC System with Tunable UV detector
• Symmetry C18 columns (3.9×150 mm, 4.6×150 mm, 4.6×100 mm; 5 μm and 3.5 μm)
• XBridge C18 4.6×100 mm, 3.5 μm
• XSelect HSS T3 4.6×150 mm, 3.5 μm
• Empower 4 Chromatography Data System

Main Results and Discussion

All adjusted methods met or exceeded the system suitability resolution requirement (NLT 1.5) for the critical abacavir impurity pair. Relative retention times were consistent for identical stationary phases, with predictable shifts for different chemistries, confirmed by PDA spectral analysis. Estimated and measured backpressures remained below the 10,000 psi limit of the Alliance iS system. Adopting 3.5 μm particles and new column dimensions yielded substantial reductions in analysis time, solvent consumption, and sample volume.

Practical Benefits and Applications

• Regulatory alignment with USP <621> harmonization
• Flexibility to adopt modern column formats and particle sizes
• Time, solvent, and sample savings through optimized gradients
• High backpressure tolerance enabling high-efficiency separations

Future Trends and Opportunities

Advances in sub-2 μm and core-shell particles, novel stationary phases, and AI-driven method optimization tools will further simplify method translation and modernization. Wider application to additional pharmacopeial monographs and integration with automated calculators and predictive software will promote industry-wide adoption of modern HPLC practices.

Conclusion

Applying USP <621> gradient allowances on the Alliance iS HPLC System enables seamless modernization of the abacavir sulfate monograph without compromising system suitability. This approach enhances analytical performance, regulatory compliance, and operational efficiency while avoiding full method revalidation.

References

• General Chapter <621> Chromatography, USP, Official Date: 01-Dec-2022.
• Abacavir Sulfate Monograph, USP-NF, Official: 01-May-2020.
• Preparative OBD Column Calculator, Waters, accessed 01/06/2023.
• Columns Calculator 2.0, Waters, accessed 01/06/2023.