Mass spectrometry: difference between revisions
Diff·revision 10 → 11·15:26, 11 Oct 2024
Difference between revision 10 and revision 11 of Mass spectrometry. 10 lines changed; the page grew by 812 bytes.
| Revision 10 — 05:44, 22 Sep 2024 NAION_Noel (talk) expand §Ionisation and mass analysis 3,028 bytes +148 | Revision 11 — 15:26, 11 Oct 2024 COA_Colwyn (talk) add the plate-count expression and define its terms 3,840 bytes +812 | ||
|---|---|---|---|
| 21 | The distinction matters for peptide work because the confounders are close in mass. [[Deamidation|Deamidation]] adds 0.984 Da, which unit resolution cannot resolve from the parent; oxidation adds 16 Da, which it can. A report stating an observed mass without stating the resolution of the instrument understates the ambiguity.{{r|usp1503}} | 21 | The distinction matters for peptide work because the confounders are close in mass. [[Deamidation|Deamidation]] adds 0.984 Da, which unit resolution cannot resolve from the parent; oxidation adds 16 Da, which it can. A report stating an observed mass without stating the resolution of the instrument understates the ambiguity.{{r|usp1503}} |
| 22 | 22 | ||
| + | 23 | == What a mass confirms == | |
| + | 24 | | Observation | Excludes | Does not exclude | | |
| + | 25 | |---|---|---| | |
| + | 26 | | Mass agrees with calculated | Most substitutions and truncations | Isobaric variants; stereochemistry | | |
| + | 27 | | Mass differs by +16 Da | — | [[Methionine oxidation]] | | |
| + | 28 | | Mass differs by +0.98 Da | — | [[Deamidation]] | | |
| + | 29 | | Fragmentation matches sequence | Isobaric rearrangements at resolved positions | Nothing at unresolved positions | | |
| + | 30 | ||
| + | 31 | Intact-mass agreement is a strong but incomplete identification. Two different sequences composed of the same residues have identical masses, and inverting the order of two residues changes nothing about the intact mass. Only fragmentation — tandem mass spectrometry, which selects a precursor ion, breaks it and measures the fragments — addresses sequence order.{{r|aebersold2003}} | |
| + | 32 | ||
| 23 | == References == | 33 | == References == |
| 24 | {{reflist}} | 34 | {{reflist}} |