Metoprolol and Select Impurities Analysis Using a Hydrophilic Interaction Chromatography Method with Combined UV and Charged Aerosol Detection

Significance of the Topic

The accurate profiling of pharmaceutical impurities is critical to ensure drug safety, efficacy, and regulatory compliance. Metoprolol succinate is widely prescribed for hypertension and angina, and several related impurities lack UV chromophores, complicating their quantification by conventional HPLC–UV methods.

Objective and Study Overview

This study aimed to develop a rapid, isocratic hydrophilic interaction chromatography (HILIC) method coupled with both UV and charged aerosol detection (CAD) for simultaneous quantification of metoprolol and three European Pharmacopoeia–defined impurities (A, M, N). The approach sought to overcome limitations of thin‐layer chromatography (TLC) and improve detection of nonchromophoric analytes without derivatization.

Methodology and Instrumentation

A Vanquish UHPLC system was employed, integrating:

• Binary pump, split‐loop autosampler, column compartment
• Diode array detector (DAD) with LightPipe™ technology (280 nm)
• Charged aerosol detector (CAD) tuned for nonvolatile analytes

Chromatographic conditions:

• Stationary phase: Two Acclaim™ Trinity™ P2 columns (3 µm, 3 × 50 mm and 3 × 100 mm) in series, combining HILIC, anion‐exchange, and cation‐exchange retention
• Mobile phase: Isocratic 100 mM ammonium formate buffer (pH 3.7) and acetonitrile (organic ratio optimized for CAD sensitivity)
• Flow rate: 1.0 mL/min; column temperature: 40 °C; injection volume: 5 µL

Standards preparation:

• Stock solutions (1.00 mg/mL) in methanol
• Working solutions ranging from 0.5 to 100 µg/mL in 50:50 water/acetonitrile for calibration

Main Results and Discussion

Baseline separation of metoprolol and impurities A, M, N was achieved within 10 minutes. UV detection at 280 nm monitored metoprolol and chromophoric impurity A, while CAD provided universal response for all analytes. Limits of detection (LOD) by CAD were 2.5 ng on column for metoprolol and impurity A, and 10–25 ng for impurities M and N. Calibration curves exhibited high linearity (R² > 0.994) with polynomial fitting for CAD and linear fitting for UV.

Benefits and Practical Applications of the Method

• Fast, isocratic HILIC separation reduces analysis time to under 10 minutes
• Combined UV/CAD detection enables quantification of both chromophoric and nonchromophoric impurities without derivatization
• CAD offers wide dynamic range and consistent response independent of analyte chemistry
• Method replaces TLC-based EP procedures, enhancing quantitative reliability at trace levels

Future Trends and Applications

As pharmaceutical analytics advances, HILIC–CAD methods may be extended to other nonchromophoric drug impurities and degradants. Integration with mass spectrometry could further enhance structural confirmation. Development of greener mobile phases and automated workflows will support high‐throughput quality control environments. The adaptability of mixed‐mode columns promises broader applications in complex drug formulations and biological matrices.

Conclusion

A robust, isocratic HILIC method using combined UV and CAD detection was demonstrated for metoprolol and three EP impurities. The approach delivers rapid, sensitive, and accurate impurity profiling, aligning with pharmacopeial modernization efforts and replacing less reliable TLC techniques.

References

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