Karl Fischer titration: difference between revisions
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| Revision 27 — 06:35, 26 Nov 2024 SemaglutideSasha (talk) rm unsourced claim per PP:V 5,150 bytes +148 | Revision 28 — 18:19, 4 Dec 2024 TFA_Counterion (talk) rv — see talk 5,998 bytes +848 | ||
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| 53 | {{note|Sample handling dominates the error budget. Lyophilised peptide is hygroscopic; a sample weighed in ambient laboratory air for two minutes can gain enough water to shift the result by a percentage point. Compendial procedure requires transfer under dry conditions, and reported values are only as good as that transfer.}} | 53 | {{note|Sample handling dominates the error budget. Lyophilised peptide is hygroscopic; a sample weighed in ambient laboratory air for two minutes can gain enough water to shift the result by a percentage point. Compendial procedure requires transfer under dry conditions, and reported values are only as good as that transfer.}} |
| 54 | 54 | ||
| + | 55 | == Interferences == | |
| + | 56 | The method responds to water, but several classes of compound produce apparent water or consume iodine independently: | |
| + | 57 | ||
| + | 58 | * '''Aldehydes and ketones''' form acetals with methanol, releasing water and giving a slow, non-terminating endpoint. Ketone-specific reagents substituting methanol are available. | |
| + | 59 | * '''Thiols and sulfides''' reduce iodine directly and inflate the result. | |
| + | 60 | * '''Basic and acidic samples''' shift the reaction pH out of the stoichiometric window. | |
| + | 61 | * '''Strongly bound water''' may not be released at cell temperature; an oven accessory that thermally desorbs water into the cell under dry carrier gas addresses this and is the usual arrangement for peptides with tightly bound hydration. | |
| + | 62 | ||
| 55 | == References == | 63 | == References == |
| 56 | {{reflist}} | 64 | {{reflist}} |
| ⋮ | ⋮ | ||
| 58 | <ref name="usp1503">United States Pharmacopeia, General Chapter <1503>, "Quality Attributes of Synthetic Peptide Drug Substances" (informational). USP–NF, current revision.</ref> | 66 | <ref name="usp1503">United States Pharmacopeia, General Chapter <1503>, "Quality Attributes of Synthetic Peptide Drug Substances" (informational). USP–NF, current revision.</ref> |
| 59 | <ref name="scholz1984">Scholz E. ''Karl Fischer Titration: Determination of Water''. Springer, Berlin (1984). The standard monograph on reagent chemistry and interferences.</ref> | 67 | <ref name="scholz1984">Scholz E. ''Karl Fischer Titration: Determination of Water''. Springer, Berlin (1984). The standard monograph on reagent chemistry and interferences.</ref> |
| + | 68 | ||
| + | 69 | == See also == | |
| + | 70 | * [[Loss on drying]] | |
| + | 71 | * [[Peptide content]] | |
| + | 72 | * [[Certificate of analysis]] | |
| + | 73 | * [[Trifluoroacetate counterion]] | |
| 60 | 74 | ||
| 61 | {{DEFAULTSORT:Karl Fischer titration}} | 75 | {{DEFAULTSORT:Karl Fischer titration}} |