Peptide intact-mass check: expected charge envelope plus a persistent +22 Da series
I am reviewing an ESI intact-mass run for a synthetic peptide. The deconvoluted neutral mass matches expectations within tolerance, and the raw spectrum shows the expected multiply-charged envelope. A second, lower-intensity series appears consistently about +22 Da relative to the corresponding charge states. My first thought is a sodium adduct, but I want to rule out a deconvolution artifact or a sample-preparation issue before including that in the report. The blank is clean, the series weakens after fresh desalting, and it is more prominent in one buffer. Would you confirm the assignment through exact spacing across charge states, targeted MS/MS, alternative adduct conditions, or a different deconvolution setup first? Also curious how you report identity confidence when the main mass is correct but adducting is obvious.