Straightforward implementation of a compendial LC method for metolazone impurity analysis with the Vanquish Core HPLC system

Significance of the topic

The control of impurities in active pharmaceutical ingredients is critical for ensuring patient safety and maintaining regulatory compliance. Compendial methods published in pharmacopeial monographs provide validated protocols that streamline quality control processes, reducing time and resources required for method development.

Objectives and study overview

This application brief demonstrates the straightforward implementation of the European Pharmacopoeia method for metolazone impurity analysis using the Thermo Scientific Vanquish Core HPLC system. The study aims to verify system suitability, chromatographic resolution, and repeatability for routine quality control of metolazone and its five specified impurities.

Methodology and instrumentation

Sample Preparation:
3 mg of the Ph. Eur. reference standard containing metolazone and impurities A–E was dissolved in 1 mL methanol according to monograph instructions.

Chromatographic Conditions:

• Column: Hypersil ODS C18, 4.6 × 250 mm, 5 µm, 120 Å
• Mobile phase A: 5.44 g/L KH2PO4 in water
• Mobile phase B: Methanol
• Gradient: 0–5 min at 30% B; 5–25 min to 50% B; hold to 35 min; return to 30% B by 38 min; re-equilibrate to 48 min
• Flow rate: 1.5 mL/min
• Column temperature: 30 °C; autosampler: 8 °C
• Detection: UV at 230 nm, 4 nm bandwidth, 5 Hz data rate, 1 s response
• Injection volume: 10 µL; needle wash off

Instrumentation:

• Vanquish Core Quaternary System Base
• Quaternary Pump C
• Split Sampler CT
• Column Compartment C
• Diode Array Detector CG
• Standard 10 mm flow cell (13 µL)
• Chromeleon CDS v7.3 for data acquisition and processing

Main results and discussion

Six replicate injections yielded baseline separation of metolazone and impurities A–E. Resolution criteria from the Ph. Eur. monograph were exceeded, with resolution values of 2.6 for E/C and 1.9 for A/B versus minimum requirements of 1.6 and 1.5, respectively. Relative standard deviations for retention times ranged from 0.02% to 0.04%, and peak area RSDs were between 0.4% and 0.6%, demonstrating excellent repeatability.

Benefits and practical applications

The validated compendial method was implemented without modification, ensuring regulatory compliance and reducing method development overhead. The Vanquish Core HPLC system delivered robust performance suitable for routine pharmaceutical quality control, offering:

• High resolution and reproducibility
• Ease of method transfer and validation
• Efficient throughput with minimal downtime

Future trends and potential applications

Advancements in HPLC technology and data systems will further enhance routine impurity profiling. Emerging trends include:

• Integration of mass spectrometric detectors for structural confirmation
• Use of greener solvents and sustainable workflows
• Automation and digitalization of data processing and reporting
• Application of advanced stationary phases for shorter run times and improved separation

Conclusion

The Vanquish Core HPLC system successfully executed the Ph. Eur. monograph method for metolazone impurity analysis, achieving all system suitability criteria and delivering reliable, repeatable results. This implementation provides a streamlined solution for pharmaceutical quality control laboratories.

Reference list

1. European Pharmacopoeia, 9th edition (2018), monograph 1757: Metolazone.
2. European Directorate for the Quality of Medicines & HealthCare; European Pharmacopoeia Online.