{"id":4094,"date":"2026-10-11T06:35:03","date_gmt":"2026-10-11T06:35:03","guid":{"rendered":"https:\/\/nhdbio.com\/?page_id=4094"},"modified":"2026-10-15T03:51:47","modified_gmt":"2026-10-15T03:51:47","slug":"adduits-sodium-potassium-en-spectrometrie-de-masse-peptidique","status":"publish","type":"page","link":"https:\/\/nhdbio.com\/fr\/analytical-methods\/peptide-ms-sodium-potassium-adducts\/","title":{"rendered":"Pics suppl\u00e9mentaires dans le spectre de masse : explication des adduits sodium et potassium"},"content":{"rendered":"

A mass spectrum has a second peak about 22 units above the first. Has the peptide gained an impurity? One possible explanation is a sodium adduct: the same molecule has formed a different ion. We will use a simple example to see the difference.<\/p>\n

The instrument detects ions<\/h2>\n

In a positive-ion spectrum, a molecule may form an ion by gaining a proton. We write that as [M+H]+, where M represents the neutral molecule. It may also form [M+Na]+ or [M+K]+ with sodium or potassium.<\/p>\n

These signals can represent different ions of the same molecule, rather than three different peptide sequences.<\/p>\n

\"Figure
Figure 1. One molecule can form proton, sodium and potassium adduct ions.<\/figcaption><\/figure>\n

Calculate three single-charge signals<\/h2>\n

For a teaching neutral mass of 1,000.0000 Da, the approximate m\/z values are 1,001.0073 for [M+H]+, 1,022.9892 for [M+Na]+ and 1,038.9632 for [M+K]+.<\/p>\n

The sodium signal is about 21.9819 above the proton signal. The potassium signal is about 37.9559 above it. Each difference compares two matching single-charge ions.<\/p>\n

\"Figure
Figure 2. Example single-charge adduct positions for a 1,000 Da molecule.<\/figcaption><\/figure>\n

Why charge changes the apparent gap<\/h2>\n

The horizontal axis is m\/z: mass divided by charge. If sodium replaces one proton in otherwise matching double-charge ions, the gap is about 21.9819 \u00f7 2 = 10.9910 m\/z.<\/p>\n

Before using an expected gap, check the charge and the actual ion formulas. Do not compare unrelated peaks simply because their spacing looks familiar.<\/p>\n

A plausible gap is a clue, not a final answer<\/h2>\n

Check the full pattern, isotope clusters and the chromatographic region in which the signals occur. Background signals or another molecule can complicate the picture.<\/p>\n

Adding the heights of these ions does not give an HPLC purity percentage. They are different measurements.<\/p>\n

\"Figure
Figure 3. Use charge and the surrounding signals to investigate an extra peak.<\/figcaption><\/figure>\n

Check the charge before calculating<\/h2>\n

A useful report names the proposed ions instead of leaving the reader to guess from peak spacing alone.<\/p>\n

For matching double-charge ions, what gap follows one sodium-for-proton replacement?<\/strong><\/p>\n
\nSee the answer<\/summary>\n

About 10.9910 m\/z. This calculation assumes that specific replacement and a charge of two.<\/p>\n<\/details>\n<\/div>\n

Reading KPV or MOTS-c spectra<\/h2>\n

For KPV or MOTS-c spectra, ask which peaks were assigned to the target molecule and which adducts were considered. An extra peak needs an explanation, but it is not automatically a new impurity.<\/p>\n

KPV<\/a> \/ MOTS-c<\/a><\/p>\n

Discuss material and document requirements with NHD<\/a> \u00b7 Continue with the analytical guide<\/a><\/p>\n