{"id":5711,"date":"2026-11-10T07:55:33","date_gmt":"2026-11-10T07:55:33","guid":{"rendered":"https:\/\/nhdbio.com\/?p=5711"},"modified":"2026-11-10T08:00:16","modified_gmt":"2026-11-10T08:00:16","slug":"peptide-ms-sodium-potassium-adduct-peaks-explained","status":"publish","type":"post","link":"https:\/\/nhdbio.com\/fr\/peptide-ms-sodium-potassium-adduct-peaks-explained\/","title":{"rendered":"Des signaux suppl\u00e9mentaires \u00e0 22 ou 38 en spectrom\u00e9trie de masse : le peptide a-t-il chang\u00e9 ?"},"content":{"rendered":"
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Peptide MS Adducts: Explaining Extra Signals at 22 or 38<\/h2>\n

Next to the expected peptide peak, some regularly spaced signals appear. They may be related to sodium or potassium adducts, or they may have other causes. Before judging, first check whether the instrument's horizontal axis is mass or mass-to-charge ratio, then confirm the ion's charge.<\/p>\n

\"Peptide
Editorial illustration of the research topic, not an experimental photograph.<\/figcaption><\/figure>\n

Start with the simplest kind of ion<\/h3>\n

Let the neutral peptide be M. The common singly charged protonated ion is written [M+H]\u207a, and the singly charged sodium adduct ion is written [M+Na]\u207a. Comparing these two ions, sodium replaces one proton, so the difference is not the mass of a sodium atom itself but about 21.9819 Da. The corresponding difference for potassium replacing a proton is about 37.9559 Da. What is described here is the mass difference between specific ion forms, not a spacing that every extra peak should have. [1]<\/a> [3]<\/a><\/p>\n

With two charges, the spacing on the horizontal axis gets smaller<\/h3>\n

Mass spectrometry commonly uses m\/z as the horizontal axis, that is, the relationship between mass and charge number. For two ions of the same charge state in which sodium replaces a proton once, if the charge number is 2, the expected spacing is about 21.9819\u00f72=10.9910 m\/z units. The corresponding spacing for one potassium replacement is about 18.9779. You cannot see peaks about 11 apart in the doubly charged region and describe it as a neutral molecular weight difference of only 11 Da. [2]<\/a><\/p>\n

\"Theoretical
Theoretical approximate values and ion assignment teaching, not measured spectra; ion form and charge must be confirmed first.<\/figcaption><\/figure>\n
\nTheoretical difference for one metal replacing a proton<\/summary>\n