Area percent purity: difference between revisions
Diff·revision 14 → 15·23:52, 20 Feb 2025
Difference between revision 14 and revision 15 of Area percent purity. 4 lines changed; the page grew by 544 bytes.
| Revision 14 — 14:16, 4 Feb 2025 AAA_Analyst (talk) add the sample preparation, since the result depends on it 6,025 bytes +26 | Revision 15 — 23:52, 20 Feb 2025 TallySheetTad (talk) add the plate-count expression and define its terms 6,569 bytes +544 | ||
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| 41 | ; Everything that was never dissolved : The determination is performed on the injected solution. Material that did not dissolve is not in it, so an appearance observation on reconstitution is a separate finding from a purity figure and has to be reported separately. | 41 | ; Everything that was never dissolved : The determination is performed on the injected solution. Material that did not dissolve is not in it, so an appearance observation on reconstitution is a separate finding from a purity figure and has to be reported separately. |
| 42 | 42 | ||
| + | 43 | The last point generalises: '''a purity assay measures what went into the injector.''' Any statement about the vial requires a separate determination of how much of the vial the injected material represented. | |
| + | 44 | ||
| 43 | === A worked example === | 45 | === A worked example === |
| 44 | A certificate reports 99.0% area percent for a 5 mg vial of a peptide. Suppose, as is ordinary for a lyophilised trifluoroacetate salt, that the vial also holds 5% water by mass and that trifluoroacetate accounts for 12% of the mass of the remaining solid. | 46 | A certificate reports 99.0% area percent for a 5 mg vial of a peptide. Suppose, as is ordinary for a lyophilised trifluoroacetate salt, that the vial also holds 5% water by mass and that trifluoroacetate accounts for 12% of the mass of the remaining solid. |
| 45 | 47 | ||
| 46 | The peptide mass is then 5 mg × 0.95 × 0.88 = 4.18 mg, or 83.6% of the nominal fill. The purity figure of 99.0% is unaffected by either the water or the counterion, because neither is integrated in the chromatogram. Both figures are correct and they describe different things. | 48 | The peptide mass is then 5 mg × 0.95 × 0.88 = 4.18 mg, or 83.6% of the nominal fill. The purity figure of 99.0% is unaffected by either the water or the counterion, because neither is integrated in the chromatogram. Both figures are correct and they describe different things. |
| + | 49 | ||
| + | 50 | Reading 99.0% as "4.95 mg of peptide" overstates the content by roughly 18%. This arithmetic is the whole reason [[Peptide content]] exists as a separate determination, and it is why a purity figure and a content figure appearing together on one certificate — 99% and 83% — are consistent rather than contradictory.{{r|usp1503}} | |
| 47 | 51 | ||
| 48 | == References == | 52 | == References == |