A Simple and Robust Method for Determination of Azadirachtin, Nimbin and Salannin in Neem Oil

Significance of the Topic

Neem oil, derived from Azadirachta indica seeds, has gained global attention for its potent insecticidal properties, low mammalian toxicity and ecological compatibility. Quantitative analysis of its main bioactive limonoids—azadirachtin-A, azadirachtin-B, nimbin and salannin—is critical for ensuring product quality, standardizing formulations and studying degradation pathways during storage.

Objectives and Study Overview

The main aim of this study was to develop a simple, rapid and robust HPLC method capable of simultaneously determining four key limonoids at nanogram levels in raw neem oil. Secondary goals included validating linearity, limits of quantitation, precision and assessing the method’s applicability across diverse sample batches collected from different regions of India.

Methodology and Instrumentation

A combined solid‐phase extraction (SPE) and reversed‐phase liquid chromatography approach was adopted for sample cleanup and separation.

• Sample Preparation: Approximately 5 g of neem oil was dissolved in methanol–water (90:10), sonicated, deep‐frozen, centrifuged and the supernatant passed through an SPE cartridge. Elution was performed with methanol–water (90:10).
• Chromatographic Conditions: Shim-pack GIST C18 column (250 × 4.6 mm, 5 µm) with a gradient of water (A) and acetonitrile (B) at 1.0 mL/min. The program ramped B from 35% to 85% over 35 min, held, then re‐equilibrated to 35% by 50 min. Injection volume was 20 µL at ambient temperature.
• Detection: Photodiode array detector set at 215 nm.

Main Results and Discussion

Calibration curves for all four analytes exhibited excellent linearity (r2 ≥ 0.9990). The limit of quantitation was 0.5 ppm for azadirachtin-A and ‑B, and 0.2 ppm for nimbin and salannin, with signal‐to‐noise ratios exceeding 50 and relative standard deviations below 2% at LOQ level. Chromatograms demonstrated clear resolution of all peaks without matrix interference after SPE cleanup. Application to real samples revealed azadirachtin content ranging from 200 to 1000 mg/kg, nimbin from 2500 to 5000 mg/kg, and salannin from 3500 to 6000 mg/kg. Stability studies indicated progressive degradation of azadirachtin-A to azadirachtin-B or overall loss when stored at ambient conditions for 1–2 months.

Benefits and Practical Applications

This analytical protocol offers high throughput automation, minimal solvent consumption and robust performance across varying sample matrices. It serves quality control laboratories in agriculture, pharmaceutical research and commercial producers of neem‐derived biopesticides and cosmetics.

Future Trends and Applications

Potential future directions include coupling with mass spectrometric detection for enhanced sensitivity and structural confirmation, expansion to additional limonoid profiles, real‐time monitoring of degradation kinetics, and miniaturized on‐site testing devices for field quality assurance.

Conclusion

A straightforward SPE‐HPLC‐PDA method using the Shimadzu LC-2030C 3D system was successfully validated for the quantitation of key neem limonoids. It exhibits excellent sensitivity, reproducibility and applicability to diverse oil samples, supporting both research and industrial quality control needs.

References

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