Determination of gentamicin and related impurities in gentamicin sulfate using simple eluents

Importance of the Topic

The accurate determination of gentamicin and its related impurities is critical for ensuring the safety, potency, and regulatory compliance of pharmaceutical formulations. Gentamicin sulfate, a widely used aminoglycoside antibiotic, requires rigorous quality control to verify its composition and impurity profile according to United States Pharmacopeia (USP) and European Pharmacopeia (EP) monographs. Simplifying the chromatographic method and reducing analysis time can enhance laboratory throughput and method robustness.

Objectives and Study Overview

This study aimed to develop and validate two modified ion-pairing HPLC methods using a Thermo Scientific Dionex IonPac AmG-3 µm C18 column to simplify eluent preparation and accelerate gentamicin analysis. Method A employs 100 mM trifluoroacetic acid (TFA) as the mobile phase, while Method B adds 2 % acetonitrile to the TFA eluent to shorten run time. Both methods replace the USP/EP post-column reagent (0.5 M NaOH) with 0.76 M NaOH.

Used Instrumentation

• Dionex ICS-5000+ or ICS-6000 HPIC system with DP pump and DC detector modules
• Electrochemical detection using a Pulsed Amperometric Detector (gold working electrode, Ag/AgCl reference)
• Dionex IonPac AmG-3 µm C18 guard (4 × 30 mm) and separation (4 × 150 mm) columns
• Chromeleon 7.2.5 Chromatography Data System

Methodology

The column temperature was maintained at 35 °C, flow rate at 0.8 mL/min, and injection volume at 20 µL. Method A used 100 mM TFA eluent; Method B used 100 mM TFA with 2 % acetonitrile. A post-column addition of 0.76 M NaOH (0.3 mL/min) provided optimal PAD pH. A four-potential carbohydrate waveform was applied for detection. System suitability was assessed with a standard mixture of gentamicin congeners (C1, C1a, C2, C2a, C2b) and sisomicin.

Main Results and Discussion

Both methods achieved resolution >4.0 between critical congeners (C2/C2b) and >2.6 between sisomicin and C1a, exceeding USP/EP criteria (resolution >1.5 and >1.2, respectively). Signal-to-noise ratios for 10 µg/mL sisomicin exceeded 240. Method A completed separation in 65 min, while Method B shortened run time to 25 min without loss of resolution. Sample #1 met all USP composition and impurity acceptance limits; Sample #2 exceeded sisomicin and total impurity thresholds, consistent with earlier findings.

Benefits and Practical Applications

• Simplified eluent preparation without pH adjustment saves time and resources.
• Method B reduces analysis time by over 60 % while maintaining chromatographic performance.
• High method robustness under acidic conditions due to column resistance to low pH.
• Applicable for routine QC of gentamicin sulfate in pharmaceutical quality control laboratories.

Future Trends and Opportunities

Advancements may include coupling these modified eluents with ultra-high-pressure liquid chromatography (UHPLC) for even faster throughput, exploring alternative stationary phases for improved selectivity, and integrating on-line impurity monitoring systems. The methodology could be extended to other aminoglycosides or multi-antibiotic formulations for comprehensive quality screening.

Conclusion

The two modified HPLC methods utilizing simple TFA-based eluents on the Dionex IonPac AmG-3 µm C18 column meet or exceed USP/EP performance requirements for gentamicin and its impurities. Method A offers straightforward eluent preparation, while Method B significantly accelerates analysis time without compromising resolution, providing effective workflows for pharmaceutical analysis.

References

1. United States Pharmacopeia. Gentamicin Sulfate. USP 40-NF 35, 2017, pp. 4391.
2. European Pharmacopoeia. Gentamicin Sulfate Monograph. EP 8.0, 2012, pp. 2326–2328.
3. United States Pharmacopeia. Gentamicin Sulfate In-process Revision. USP 43(3), 2018.
4. Hu J., Rohrer J. Thermo Scientific Application Note 72647: Determination of gentamicin and related impurities in gentamicin sulfate.
5. Thermo Scientific. Dionex IonPac AmG-3 µm C18 Columns Product Manual, P/N 065728, 2017.
6. Thermo Scientific. Dionex ICS-5000+ Ion Chromatography System Operator’s Manual, P/N 065446, 2014.
7. Thermo Scientific. Electrochemical Detection User’s Compendium, P/N 065340-02, 2013.
8. Thermo Scientific. ED40 Electrochemical Detector Operator’s Manual.
9. United States Pharmacopeia General Chapter <1225>, Validation of Compendial Methods, USP 40, 2018.
10. United States Pharmacopeia General Chapter <621>, Chromatography, USP 37, 2014.