Analyzing Iohexol by Compendial Method Produces Excellent Precision with Shallow Gradients Using an Agilent 1260 Infinity III LC

Significance of the topic

Compendial methods defined by major pharmacopoeias establish standardized procedures for pharmaceutical quality control, ensuring consistent and reproducible results across laboratories.
Iohexol, a polar X-ray contrast agent, requires a shallow gradient liquid chromatography separation that challenges LC hardware to deliver precise retention times and resolution under highly aqueous conditions.

Study objectives and overview

This application note evaluates the performance of the Agilent 1260 Infinity III LC system for the compendial analysis of iohexol according to the European Pharmacopoeia monograph.
It then adapts the method to UHPLC conditions to reduce analysis time and solvent consumption while maintaining all system suitability criteria.

Methodology

The original method applied a binary gradient from 1 to 13 % acetonitrile over 60 minutes at 1 mL/min on a 4.6 × 250 mm, 5 µm C18 column, with UV detection at 254 nm and system suitability assessed via resolution and retention time RSD over eight injections.
Gradient slope, flow rate, column dimensions, and injection volume were then adjusted within pharmacopeial transfer limits to operate on a 3 × 150 mm superficially porous C18 column (2.7 µm) at 0.788 mL/min, shortening runtime and reducing solvent usage.

Used instrumentation

• Agilent InfinityLab Assist Upgrade (G7178A) with Assist Interface (G7179A) and Assist Hub (G7180A)
• Agilent 1260 Infinity III Quaternary Pump (G7111B)
• Agilent 1260 Infinity III Vialsampler (G7129A) with integrated column compartment and 3 µL heat exchanger (option #063) plus sample thermostat (option #101)
• Agilent 1260 Infinity III Variable Wavelength Detector (G7114A) with 10 mm standard flow cell (option #018)
• Agilent OpenLab CDS software, revision 2.7 or later

Main results and discussion

The compendial method achieved baseline separation of iohexol endo/exo isomers and impurities A and J, with resolution ≥3.8 and retention time RSD ≤0.083 % (n=8).
Under optimized UHPLC conditions, the total runtime was reduced from 75 to 27 minutes (64 % reduction) and solvent usage fell by 71 %, while resolution remained ≥2.1 and RSD improved to ≤0.044 %.

Benefits and practical applications

• High retention time precision under challenging shallow gradients
• Compliance with pharmacopeial system suitability criteria
• Significant reduction in analysis time and solvent consumption
• Enhanced laboratory throughput and cost efficiency
• Improved sustainability through lower solvent usage

Future trends and opportunities

Advances in high-precision quaternary pumps and superficially porous column technologies will support further miniaturization and green chromatography.
Automated method transfer protocols and AI-driven optimization may streamline method development and ensure robust performance.
The growing emphasis on sustainable laboratory workflows will drive wider adoption of low-solvent, high-throughput analytical strategies.

Conclusion

The Agilent 1260 Infinity III LC system delivers excellent retention time precision and meets compendial resolution requirements under a shallow gradient for iohexol analysis.
Method transfer to UHPLC conditions yielded a 64 % runtime reduction and a 71 % decrease in solvent use while preserving system suitability, demonstrating a balance of compliance, efficiency, and sustainability.

References

1. The United States Pharmacopoeia. General chapter <1226> Verification of Compendial Procedures, 2019.
2. The European Pharmacopoeia 11.0, Iohexol. 01/2017:1114.
3. National Drug Code Directory, United States Food and Drug Administration.
4. The United States Pharmacopoeia. General chapter <621> Chromatography, 2023.
5. The European Pharmacopoeia 11.0, Chapter 2.2.46, Chromatographic Separation Techniques.
6. Schipperges, S.; Naegele, E. Reduce the Cost per Injection for Your USP Compendial Method. Agilent application note 5994-5897EN, 2023.
7. Fu, R.; Wei, T. Analysis of Polar Compounds Using an Agilent InfinityLab Poroshell 120 Aq-C18 Column. Agilent application note 5994-5555EN, 2022.