Trifluoroacetate counterion: difference between revisions
Diff·revision 5 → 6·19:45, 28 Oct 2024
Difference between revision 5 and revision 6 of Trifluoroacetate counterion. 2 lines changed; the page grew by 343 bytes.
| Revision 5 — 22:49, 20 Oct 2024 AmylinAmos (talk) ce 2,370 bytes ±0 | Revision 6 — 19:45, 28 Oct 2024 PeakShapePol (talk) add the sample preparation, since the result depends on it 2,713 bytes +343 | ||
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| 11 | The counterion pairs with basic side chains — lysine, arginine, histidine — and with the N-terminal amine, so its mass fraction depends on how many basic residues the sequence carries. For a peptide with several, trifluoroacetate can be a substantial fraction of the solid, commonly cited in the range of 5–25%.{{r|roux2008}} | 11 | The counterion pairs with basic side chains — lysine, arginine, histidine — and with the N-terminal amine, so its mass fraction depends on how many basic residues the sequence carries. For a peptide with several, trifluoroacetate can be a substantial fraction of the solid, commonly cited in the range of 5–25%.{{r|roux2008}} |
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| + | 13 | This matters because that mass is not peptide. A vial containing 5 mg of solid at 15% trifluoroacetate and 6% water contains under 4 mg of peptide even at high chromatographic purity — which is why [[Peptide content|peptide content]] and [[Area percent purity|purity]] are separate determinations answering separate questions.{{r|usp1503}} | |
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| 13 | == Origin and removal == | 15 | == Origin and removal == |
| 14 | Trifluoroacetic acid is used as an ion-pairing modifier because it sharpens peptide peaks considerably; the resulting separation is better than with most alternatives. It is also used in the cleavage step of [[Solid-phase peptide synthesis|Fmoc synthesis]], so the peptide encounters it twice.{{r|usp1503}} | 16 | Trifluoroacetic acid is used as an ion-pairing modifier because it sharpens peptide peaks considerably; the resulting separation is better than with most alternatives. It is also used in the cleavage step of [[Solid-phase peptide synthesis|Fmoc synthesis]], so the peptide encounters it twice.{{r|usp1503}} |