Straightforward implementation of a compendial LC method for metolazone impurity analysis

Importance of the Topic

The implementation of compendial methods from pharmacopeial monographs ensures consistent quality control of active pharmaceutical ingredients. Utilizing a validated European Pharmacopoeia procedure for metolazone impurity analysis reduces development time and regulatory risk while delivering reliable, reproducible results in routine laboratory environments.

Objectives and Study Overview

This study demonstrates the seamless adoption of the European Pharmacopoeia liquid chromatography method for metolazone and its impurities on the Thermo Scientific Vanquish Core HPLC system. The analysis was performed under Waters Empower 3 control using the Thermo Scientific Standard Instrument Integration plugin, highlighting system performance in a regulated setting.

Methodology

Sample preparation followed the monograph: 3 mg of reference standard containing metolazone and impurities A–E was dissolved in 1 mL of methanol. Chromatographic separation employed a phosphate buffer–methanol gradient, with detection at 230 nm.

Instrumentation Used

• Thermo Scientific Vanquish System Base Core
• Vanquish Quaternary Pump C
• Vanquish Sampler CT
• Vanquish Column Compartment C
• Vanquish Variable Wavelength Detector C with standard flow cell, SST, 10 mm, 11 µL
• Hypersil ODS C18 column, 4.6 × 250 mm, 5 µm
• Empower 3 software with SII plugin for instrument configuration

Chromatographic Conditions

• Mobile phase A: 5.44 g/L potassium dihydrogen phosphate in water
• Mobile phase B: methanol
• Flow rate: 1.5 mL/min; gradient from 30% to 50% B (0–25 min) then back to 30% (38–48 min)
• Column temperature: 30 °C; autosampler: 8 °C; injection volume: 10 µL
• Detection: 230 nm, data rate 5 Hz, response time 1 s

Main Results and Discussion

Baseline separation of metolazone and five known impurities was achieved according to the monograph requirements. System suitability criteria were exceeded, with resolution values well above 1.6 for E/C and 1.5 for A/B. Repeatability was excellent, with retention time RSDs between 0.01% and 0.02% and peak area RSDs between 0.1% and 0.4% over six injections.

Benefits and Practical Applications

The Vanquish Core HPLC system combined with Empower 3 and SII ensures regulated control, easy method transfer, and robust performance. Laboratories can adopt the compendial method without additional development, streamlining routine quality control of metolazone formulations.

Future Trends and Applications

Integration of mass spectrometric detection, automation of sample handling, and coupling with process analytical technology are anticipated to further enhance impurity profiling. Advances in software interoperability will facilitate real-time data review and remote operation.

Conclusion

The European Pharmacopoeia method for metolazone impurity analysis was successfully implemented on the Vanquish Core HPLC platform with Empower 3 control. The system met all suitability criteria and delivered highly reproducible results, confirming its suitability for routine pharmaceutical quality control.

References

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