Karl Fischer titration: difference between revisions
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| 63 | Peptides containing free cysteine are the interference most relevant here, since a thiol-bearing sequence can give a falsely elevated water figure.{{cn}} A discrepancy between Karl Fischer and [[Loss on drying|loss-on-drying]] results on the same lot is a useful diagnostic: loss on drying measures all volatiles, so LOD substantially exceeding KF suggests [[Residual solvent|residual solvent]], whereas KF exceeding LOD suggests either an interference or water too tightly bound to be driven off at the drying temperature.{{r|usp1503}} | 63 | Peptides containing free cysteine are the interference most relevant here, since a thiol-bearing sequence can give a falsely elevated water figure.{{cn}} A discrepancy between Karl Fischer and [[Loss on drying|loss-on-drying]] results on the same lot is a useful diagnostic: loss on drying measures all volatiles, so LOD substantially exceeding KF suggests [[Residual solvent|residual solvent]], whereas KF exceeding LOD suggests either an interference or water too tightly bound to be driven off at the drying temperature.{{r|usp1503}} |
| 64 | 64 | ||
| + | 65 | == Interpretation on a certificate of analysis == | |
| + | 66 | {{main|Peptide content}} | |
| + | 67 | ||
| + | 68 | A complete mass balance for a lyophilised peptide accounts for approximately four components: | |
| + | 69 | ||
| + | 70 | | Component | Typical range (w/w) | Determined by | | |
| + | 71 | |---|---|---| | |
| + | 72 | | Peptide (net) | 78–92% | [[Amino acid analysis]] or nitrogen determination | | |
| + | 73 | | Water | 3–8% | Karl Fischer titration | | |
| + | 74 | | Counterion (TFA or acetate) | 2–12% | Ion chromatography | | |
| + | 75 | | Residual solvent, salts | <1% | Gas chromatography, ash | | |
| + | 76 | ||
| 65 | == References == | 77 | == References == |
| 66 | {{reflist}} | 78 | {{reflist}} |