{"id":4097,"date":"2026-10-11T06:35:03","date_gmt":"2026-10-11T06:35:03","guid":{"rendered":"https:\/\/nhdbio.com\/?page_id=4097"},"modified":"2026-10-15T03:51:58","modified_gmt":"2026-10-15T03:51:58","slug":"espacamento-isotopico-de-peptideo-estado-de-carga","status":"publish","type":"page","link":"https:\/\/nhdbio.com\/pt-br\/analytical-methods\/peptide-isotope-spacing-charge-state\/","title":{"rendered":"Por que os picos do espectro de massa formam um aglomerado: espa\u00e7amento isot\u00f3pico e carga"},"content":{"rendered":"

Several closely spaced peaks appear in the spectrum. Are they several impurities? They may instead be an isotope cluster from one type of molecule. The spacing can help explain the ion\u2019s charge.<\/p>\n

The same element can have slightly different masses<\/h2>\n

Atoms of the same element can have different numbers of neutrons. These versions are called isotopes. A molecule containing a heavier isotope has a slightly different mass, even when its peptide sequence has not changed.<\/p>\n

Peptides contain many atoms, so a sample can give a group of nearby isotope signals rather than a single line. Actual patterns depend on the elements and isotope combinations present.<\/p>\n

\"Figure
Figure 1. A group of isotope peaks need not represent different peptide sequences.<\/figcaption><\/figure>\n

Why more charge squeezes the gaps<\/h2>\n

The axis is m\/z: ion mass divided by charge. Using a common carbon-isotope spacing approximation of 1.00335 Da, a single-charge group has gaps near 1.00335 m\/z. With two charges, the gaps are near 0.50168; with three, near 0.33445.<\/p>\n

The mass difference is divided by a larger number. That is why the peaks move closer together on this axis.<\/p>\n

\"Figure
Figure 2. Approximate gaps for one, two and three charges.<\/figcaption><\/figure>\n

Read the scale, not just the shape<\/h2>\n

Zoom into a clearly resolved cluster and subtract the positions of adjacent peaks. A gap near 0.50 m\/z suggests two charges in this model. A gap near 0.33 suggests three.<\/p>\n

This only works if you are comparing peaks from the same cluster. Overlapping clusters or insufficient resolution can make the estimate misleading.<\/p>\n

Turn m\/z back into molecular mass<\/h2>\n

Suppose the ion is confirmed as [M+2H]2+ and its m\/z is 501.0073. Multiply by two, then subtract the mass of the two added protons: 2 \u00d7 501.0073 \u2212 2 \u00d7 1.007276 \u2248 1,000.0000 Da.<\/p>\n

Spacing helps estimate charge, but does not by itself establish the adduct type. Check the ion formula before using this calculation.<\/p>\n

\"Figure
Figure 3. For the assigned protonated ion, account for charge and added protons.<\/figcaption><\/figure>\n

Try reading a three-charge cluster<\/h2>\n

A convincing cluster can help interpret the mass signal. It does not measure peptide activity or establish every position in its sequence.<\/p>\n

Adjacent peaks are about 0.334 m\/z apart. Which charge is the first possibility in this model?<\/strong><\/p>\n
\nSee the answer<\/summary>\n

Three charges, provided the peaks belong to one suitably resolved cluster.<\/p>\n<\/details>\n<\/div>\n

Checking MOTS-c and SS-31 plots<\/h2>\n

For MOTS-c or SS-31 spectra, ask which isotope clusters and charge states support the reported molecular mass. Keep the annotated spectrum with the calculation.<\/p>\n

MOTS-c<\/a> \/ SS-31<\/a><\/p>\n

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