Mass spectrometry: difference between revisions
Diff·revision 19 → 20·19:46, 13 Mar 2025
Difference between revision 19 and revision 20 of Mass spectrometry. 6 lines changed; the page grew by 896 bytes.
| Revision 19 — 00:09, 21 Feb 2025 CiteBot (talk) bot: flag bare reference 4,327 bytes ±0 | Revision 20 — 19:46, 13 Mar 2025 RepackRadek (talk) add the cross-link to the compendial chapter 5,223 bytes +896 | ||
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| 34 | Stereochemistry is invisible to mass spectrometry entirely. A D-amino acid substitution is isobaric with the L form and requires [[Amino acid analysis|chiral analysis]] to detect. For peptides synthesised with racemisation-prone residues this is a real rather than theoretical gap. | 34 | Stereochemistry is invisible to mass spectrometry entirely. A D-amino acid substitution is isobaric with the L form and requires [[Amino acid analysis|chiral analysis]] to detect. For peptides synthesised with racemisation-prone residues this is a real rather than theoretical gap. |
| 35 | 35 | ||
| + | 36 | == Quantification == | |
| + | 37 | Mass spectrometry is not inherently quantitative. Ionisation efficiency varies by orders of magnitude between molecules and is affected by the matrix, so peak intensity does not translate into concentration without calibration against a standard of the same substance.{{r|usp1503}} | |
| + | 38 | ||
| + | 39 | Where quantification is required, the usual approach couples chromatography to mass spectrometry — [[Liquid chromatography-mass spectrometry|LC-MS]] — and calibrates against a [[Reference standard|reference standard]], ideally with an isotopically labelled internal standard. This is standard practice in bioanalysis and is not typical of the certificates seen in research-chemical supply; a quantitative claim requires a validated procedure behind it.{{r|ich_q2}} | |
| + | 40 | ||
| 36 | == References == | 41 | == References == |
| 37 | {{reflist}} | 42 | {{reflist}} |
| ⋮ | ⋮ | ||
| 39 | <ref name="usp1503">United States Pharmacopeia, General Chapter <1503>, ''Quality Attributes of Synthetic Peptide Drug Substances''.</ref> | 44 | <ref name="usp1503">United States Pharmacopeia, General Chapter <1503>, ''Quality Attributes of Synthetic Peptide Drug Substances''.</ref> |
| 40 | <ref name="usp736">United States Pharmacopeia, General Chapter <736>, ''Mass Spectrometry''.</ref> | 45 | <ref name="usp736">United States Pharmacopeia, General Chapter <736>, ''Mass Spectrometry''.</ref> |
| + | 46 | <ref name="ich_q2">International Council for Harmonisation, ''Q2(R2): Validation of Analytical Procedures'' (2023).</ref> | |
| 41 | 47 | ||
| 42 | == See also == | 48 | == See also == |