Purity determination of digitoxin by two-signal suppression-internal standard correction-high-performance liquid chromatography-quantitative nuclear magnetic resonance.

In the biomedical and chemical fields, purity assessment of compounds is a critical step in ensuring product quality and safety. In this study, a method for purity quantification was proposed as two-signal suppression-internal standard correction-high-performance liquid chromatography-quantitative nuclear magnetic resonance (TSS-ISC-HPLC-qNMR). The two-signal suppression effectively suppresses the interference of solvent signals in the NMR spectra, and the internal standard correction eliminates the influence of many variables during sample preparation and analysis. The purity result (99.89%) of the quantification of certified reference material of acesulfame (AF) by this method matched with the certified value (99.88%), which verified the accuracy of the method. The purity result (with standard deviation) of 94.42% ± 0.10% for the quantification of the low-purity drug digitoxin by the method matched with the purity result of 94.42% ± 0.11% by qNMR with deconvolution (as a validated method), which proved that the method could be used for the quantification of low-purity compounds. The methodology achieved a substantial reduction in total analysis time, from 28 to 4 h (considering only the routine analysis time after optimization), in contrast to the ISC-HPLC-qNMR approach. Additionally, it effectively decreased bias to undetectable with a standard deviation of 0.10%, while the bias of the TSS-HPLC-qNMR method was 0.93%. The present method ensures the accuracy of the quantitative results while demonstrating a low economic burden and significant time efficiency, which shows great potential for application in the accurate quantitative analysis of low-purity organic compounds.