Spectrus: Identifying and annotating impurities in NMR spectra

Description
NMR spectra often contain small impurity peaks from side products, solvents, or stabilizers. Properly identifying and annotating these peaks helps distinguish them from analyte signals.

Solution

1. Acquire and process the NMR spectrum (phase and baseline correction).
2. Identify major analyte peaks first and assign them using structure and 2D data where available.
3. Examine remaining, unassigned peaks:
   • Compare with known solvent and stabilizer tables (e.g., standard impurities in deuterated solvents).
   • Consider known or probable side products.
4. In Spectrus, using the Annotation tool, select and annotate impurity peaks:
   • Label them with a short description (e.g., “impurity”, “residual solvent”, “stabilizer”).
5. For quantitative or purity assessment:
   • Decide whether to integrate impurity peaks separately.
   • Clearly separate impurity integrals from analyte integrals.
6. Include impurity annotations in reports to clarify which signals do not belong to the main structure.