not-yet-known not-yet-known not-yet-known unknown Rationale: Stable isotope-labeled organic compounds, containing D, 15N or 13C, have widespread applications in chemistry, biology, environmental science, and agriculture. However, the isotopic purity calculations for these labeled organic compounds are usually complicated, especially in mixed isotopes-labeled scenarios. Herein, the electrospray ionization-high resolution mass spectrometry (ESI-HRMS) was applied to determinate the isotopic purity for stable isotope-labeled organic compounds, containing D, 15N or 13C. Methods: The representative isotopolog ion with its specific molecular formula was proposed to represent various labeled states. The isotopic purity was calculated with the corrected intensities of representative isotopolog ions by removing the natural isotopic contributions from preceding peaks. A unified equation has been proposed for the calculation of isotopic purity for various labeled situations including D, 15N or 13C. Results: Several case studies were presented and our calculated isotopic purities were all consistent with the isotopic purities provided in the certificate. In-source CID method was applied for the labeled compound (molecular weight＞400 u), when the maxim resolution setting was insufficient to differentiate isobaric isotopolog ions. Conclusion: Finally, a workflow with a Python calculation program was summarized for determinations of the isotopic purity for mono isotope-labeled or mixed isotopes-labeled organic compounds, involving D, 15N or 13C, by using ESI-HRMS to assigning the representative isotopolog ions with accurate mass and excluding the isobar interference.