METHOD VALIDATION FOR QUANTIFICATION OF METAMIZOLE USING QUANTITATIVE NMR (qNMR)

Quantitative Nuclear Magnetic Resonance (qNMR) spectroscopy offers a reliable approach for both structural analysis and accurate quantification of compounds, without requiring an internal standard identical to the analyte; this allows for the quantification of multiple substances using a single standard¹. Therefore, pharmaceutical industries increasingly seek reliable ways to quantify their drugs and active pharmaceutical ingredients (APIs) in order to ensure the integrity and quality of their products, and the qNMR technique presents itself as an excellent solution in this regard, as it is considered a primary analytical technique². However, to ensure reproducibility and compliance with regulatory standards, method validation is necessary. In line with the requirements of laboratories operating under Good Laboratory Practices (GLP) and the ISO/IEC 17025 standard, this study aimed to validate a qNMR method for the quantification of metamizole using ¹H NMR spectroscopy³. Metamizole was chosen because it is one of the most widely consumed drugs in Brazil, often through self-medication, making it an extremely important target for its purity to be verified through a broader range of approaches^{4 5}. Thus, the validation of the quantification method for this API by qNMR was carried out with the intention of allowing the developed method to be another one applied both in the industry, which seeks a way to control the quality of its product, and in studies. The validation process followed the guidelines outlined in the INMETRO document DOQ-CGCRE-008. Sample solutions were prepared by diluting a stock solution containing metamizole and 1,3,5-trimethoxybenzene (used as internal standard) in DMSO-d₆. All experiments were conducted using a 9.4 T Bruker^® AVANCE III spectrometer (400 MHz for ¹H frequency). Data were processed using TopSpin^® and Excel^® software. The validation parameters evaluated were selectivity, linearity, limit of detection, limit of quantification, accuracy, precision, and robustness. The results met the acceptance criteria, demonstrating that the method is fit for the initial purpose.

REFERENCES

(1)  Botros, L. et al., Connecting the Practice of Modern Qualitative and Quantitative NMR Analysis with Its Theoretical Foundation, 2025.

(2) Sousa, E.G.R. de et al., Development and Validation of ¹H Nuclear Magnetic Resonance Quantitative Method for Efavirenz API Quality Control, Current Analytical Chemistry, 2024.

(3) INMETRO, Guidelines for Analytical Method Validation, 2020.

(4) Xavier, M.S. et al., Self-medication and Health Risk: A Literature Review, Brazilian Journal of Health Review, 2021.

(5) Guimara˜es, F.P.G. et al., Dipyrone Ban Policy: A Reflection, Brazilian Journal of Health Review, 2021. 

Acknowledgements: FAPESP, CNPq and CAPES.