Analysis of Amoxicillin capsule

Significance of the Topic

Amoxicillin is one of the most commonly prescribed β-lactam antibiotics in both human and veterinary medicine. Reliable quantification of amoxicillin and its related degradation products is critical for ensuring drug safety, efficacy, and compliance with pharmacopeial standards. Analytical methods capable of separating the parent compound from closely related impurities play a key role in quality control and regulatory approval of pharmaceutical formulations.

Study Objectives and Overview

This application note describes a reverse-phase liquid chromatography method for the analysis of amoxicillin in capsule formulations using the Shim-pack GIST C18-AQ column. The study aims to demonstrate baseline separation of amoxicillin, its thiazole acid derivative, diketopiperazine impurity, and cyclic oligomers, while validating system suitability parameters under gradient elution conditions.

Instrumentation Used

• Column: Shim-pack GIST C18-AQ, 250 mm × 4.6 mm I.D., 5 μm particle size
• Vials: LabTotal Vial for LC/LCMS
• Detector: UV absorbance at 254 nm

Methodology

The chromatographic separation employed a binary gradient of 0.05 M potassium dihydrogen phosphate buffer (pH 5.0) and acetonitrile. Mobile phase A consisted of 99:1 buffer to acetonitrile, and mobile phase B was 80:20. The gradient started at 8% B, held for 12 min, increased linearly to 100% B at 37 min, maintained until 52 min, then returned to 8% B by 53 min and equilibrated until 67 min. Flow rate was 1 mL/min, column temperature 30 °C, and injection volume 20 μL. Standard and system suitability solutions were prepared at 20 μg/mL in mobile phase A.

Main Results and Discussion

Chromatograms of the standard mix, system suitability solution, and capsule extract demonstrated clear resolution of five peaks: thiazole acid, amoxicillin, diketopiperazine impurity, closed-loop dimer, and closed-loop trimer. The optimized gradient achieved complete separation within a 52 min runtime. System suitability criteria including peak symmetry, retention time reproducibility, and resolution exceeded typical acceptance thresholds, confirming method robustness.

Benefits and Practical Applications

• High resolution of amoxicillin and related impurities supports stringent quality control requirements.
• Gradient method flexibility allows adaptation for other β-lactam antibiotics or formulations.
• Reproducible retention times and peak shapes facilitate routine batch release testing.

Future Trends and Applications

Increasing demand for high-throughput and green analytical methods may drive adoption of shorter columns and more efficient stationary phases. Coupling this HPLC method with mass spectrometry detection could enhance sensitivity for trace-level impurities. Automated sample preparation and data processing will further streamline pharmaceutical QC workflows.

Conclusion

The described HPLC method using the Shim-pack GIST C18-AQ column provides a robust, reliable approach for the separation and quantitation of amoxicillin and key degradation products in capsule formulations. The gradient conditions and system parameters meet stringent system suitability requirements, making this method suitable for routine quality control.

Reference

• Shimadzu Corporation. Analysis of Amoxicillin Capsule. Application Note ERAS-1000-0067, First Edition: Mar. 2023.