Karl Fischer titration: difference between revisions
Diff·revision 5 → 6·05:17, 20 Aug 2024
Difference between revision 5 and revision 6 of Karl Fischer titration. 2 lines changed; the page grew by 314 bytes.
| Revision 5 — 15:43, 6 Aug 2024 ArchiveBot (talk) bot: flag bare reference 2,499 bytes +87 | Revision 6 — 05:17, 20 Aug 2024 SigFigSindri (talk) expand §Interpretation on a certificate of analysis 2,813 bytes +314 | ||
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| 10 | The method matters to readers of a [[Certificate of analysis|certificate of analysis]] for a specific and frequently misunderstood reason: a chromatographic purity figure is a statement about the ''relative'' composition of the material that dissolved, not about ''how much'' peptide the vial contains. Water, counterions and residual salts occupy mass. A vial of material reported at 99% purity by [[High-performance liquid chromatography|HPLC]] may nevertheless be 6% water and 8% [[Trifluoroacetate counterion|trifluoroacetate]] by mass, in which case its [[Peptide content|peptide content]] is closer to 85%.{{r|usp1503}} | 10 | The method matters to readers of a [[Certificate of analysis|certificate of analysis]] for a specific and frequently misunderstood reason: a chromatographic purity figure is a statement about the ''relative'' composition of the material that dissolved, not about ''how much'' peptide the vial contains. Water, counterions and residual salts occupy mass. A vial of material reported at 99% purity by [[High-performance liquid chromatography|HPLC]] may nevertheless be 6% water and 8% [[Trifluoroacetate counterion|trifluoroacetate]] by mass, in which case its [[Peptide content|peptide content]] is closer to 85%.{{r|usp1503}} |
| 11 | 11 | ||
| + | 12 | Two variants are in routine use. Volumetric titration delivers iodine from a burette and suits samples containing milligram quantities of water; coulometric titration generates iodine electrochemically at the anode and suits the microgram-to-low-milligram range typical of a 10 mg peptide sample.{{r|scholz1984}} | |
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| 12 | == Chemical basis == | 14 | == Chemical basis == |
| 13 | The underlying reaction is the oxidation of sulfur dioxide by iodine, which consumes water stoichiometrically: | 15 | The underlying reaction is the oxidation of sulfur dioxide by iodine, which consumes water stoichiometrically: |