Quantitative proton nuclear magnetic resonance for the structural and quantitative analysis of atropine sulfate

• We analyzed the conformation of atropine sulfate in equilibrium by NMR experiments.
• We revised quantification signal of analyte for the qNMR method described before.
• We developed a qNMR method for the calibration of atropine sulfate.
• The results from the method between qNMR and mass balance method were identical.

This study assessed a general method of quantitative nuclear magnetic resonance (qNMR) for the calibration of atropine sulfate (Active Pharmaceutical Ingredient, API) as reference standard. The spectra were acquired in D2O using maleic acid as the internal standard. Conformational behaviors of tropane ring were observed and studied by means of NMR and ROESY experiments at different temperature, which showed that the azine methyl group was at equilibrium for axial and equatorial conformations at room temperature. Signal delay and monitor signals of qNMR experimentation were optimized for quantification. The study reported here validated the method's linearity, range, limit of quantification, stability and precision. The results were consistent with the results obtained from mass balance approach.

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