Analysis of Aminoglycoside Antibiotics　(Gentamicins & Neomycin)　(1)

Importance of the Topic

Aminoglycoside antibiotics such as gentamicins and neomycin are subject to strict regulation in food and dairy products due to potential health risks. Sensitive and accurate detection of their residues in milk ensures compliance with revised standards by health authorities and supports overall food safety.

Study Objectives and Overview

This work presents a liquid chromatography–mass spectrometry method for simultaneous analysis of gentamicins C1, C2, C1a and neomycin B in accordance with Japanese Ministry of Health guidelines. The goal is to optimize chromatographic separation, improve peak quality and achieve detection limits well below regulatory thresholds.

Methodology

• Column: Shimadzu Shim-pack FC-ODS, 3.0 mm I.D. × 75 mm
• Mobile phases: 5 mM heptafluorobutyric acid in water (A) and acetonitrile (B)
• Gradient elution: start 0% B, ramp to 40% B over 15–30 min
• Flow rate: 0.4 mL/min; column temperature 40 °C; injection volume 10 µL
• ESI in positive mode; probe voltage +4.5 kV; dryer and heater at 200 °C
• Selected ion monitoring of m/z 478.3, 464.3, 450.3 (gentamicins) and 615.3 (neomycin B)

Main Results and Discussion

• Positive ESI spectra confirmed protonated molecules and diagnostic fragment ions at m/z 322 for purpurosamin and m/z 455 for neomycin.
• Gradient elution markedly improved peak shapes compared to isocratic runs with 25% acetonitrile.
• SIM chromatograms provided clear resolution of gentamicin congeners and neomycin B peaks within 10–30 min.
• Calibration curves showed excellent linearity (r2 > 0.9999) over concentration ranges down to low ppb levels.
• Sample concentration to 5× allowed detection at one tenth of the regulatory maximum residue levels without loss of peak integrity.

Benefits and Practical Applications

The method delivers high sensitivity and specificity for routine QA/QC of dairy products. Rapid analysis time, robust peak shapes and low detection limits facilitate compliance testing in industrial and regulatory laboratories.

Instrumentation Used

• Shimadzu LC system with Shim-pack FC-ODS column
• Electrospray ionization source in positive mode
• Mass spectrometer operating in SIM acquisition

Future Trends and Applications

Emerging approaches may leverage ultrahigh‐performance LC for faster run times, high‐resolution MS to resolve complex aminoglycoside mixtures and automated sample prep for field deployable screening. Integration with data analytics could further enhance monitoring efficiency.

Conclusion

The optimized LC-MS protocol offers a robust, sensitive and regulation‐compliant solution for aminoglycoside residue analysis in milk, supporting stringent food safety requirements.