Karl Fischer titration: difference between revisions
Diff·revision 6 → 7·00:20, 29 Aug 2024
Difference between revision 6 and revision 7 of Karl Fischer titration. 20 lines changed; the page grew by 1,323 bytes.
| Revision 6 — 05:17, 20 Aug 2024 SigFigSindri (talk) expand §Interpretation on a certificate of analysis 2,813 bytes +314 | Revision 7 — 00:20, 29 Aug 2024 NewLabNell (talk) state the mass accuracy in parts per million rather than daltons 4,136 bytes +1,323 | ||
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| 4 | | Classification = Titrimetric, iodine-based | 4 | | Classification = Titrimetric, iodine-based |
| 5 | | Variants = Volumetric; coulometric | 5 | | Variants = Volumetric; coulometric |
| + | 6 | <!-- Performance --> | |
| + | 7 | | Typical range (coulometric) = 10 µg – 10 mg water | |
| + | 8 | | Typical range (volumetric) = 1 mg – 500 mg water | |
| + | 9 | | Reported precision = ≈1–3% relative at 1–10% w/w | |
| + | 10 | | Sample size = 10–100 mg lyophilised solid | |
| 6 | }} | 11 | }} |
| 7 | 12 | ||
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| 20 | 25 | ||
| 21 | Two features follow from the stoichiometry and are the practical basis of the method: | 26 | Two features follow from the stoichiometry and are the practical basis of the method: |
| + | 27 | ||
| + | 28 | * the endpoint is detectable amperometrically, because excess iodine depolarises a double-platinum indicator electrode; | |
| + | 29 | * one faraday of charge liberates one mole of iodine, so in the coulometric variant the ''charge passed'' is a direct measure of water — no titrant standardisation is required. | |
| + | 30 | ||
| + | 31 | == Volumetric and coulometric variants == | |
| + | 32 | | Property | Volumetric | Coulometric | | |
| + | 33 | |---|---|---| | |
| + | 34 | | Iodine source | Titrant from burette | Generated at anode | | |
| + | 35 | | Water range | 1–500 mg | 10 µg – 10 mg | | |
| + | 36 | | Titrant standardisation | Required, daily | Not required | | |
| + | 37 | | Typical sample | 100 mg – 1 g | 10–100 mg | | |
| + | 38 | | Suits lyophilised peptides | Marginally | Yes | | |
| + | 39 | | Cell volume | 30–50 mL | 100–150 mL | | |
| + | 40 | ||
| + | 41 | For a research peptide vial nominally containing 5–10 mg of solid, only the coulometric variant is realistic: the total water present may be as little as 300 µg, which is below the practical resolution of a volumetric titration on that sample mass. Certificates reporting water content on 10 mg vials by volumetric titration should be read with that in mind.{{r|scholz1984}} | |
| 22 | 42 | ||
| 23 | == References == | 43 | == References == |