Area percent purity: difference between revisions
Diff·revision 1 → 2·05:10, 29 Aug 2024
Difference between revision 1 and revision 2 of Area percent purity. 5 lines changed; the page grew by 487 bytes.
| Revision 1 — 15:42, 28 Aug 2024 GlossaryGleb (talk) create article — method stub 1,321 bytes +1,321 | Revision 2 — 05:10, 29 Aug 2024 KarlFischerKit (talk) clarify the difference between related substances and total impurities 1,808 bytes +487 | ||
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| 7 | The measure has one defining property from which everything else follows: '''it is relative to what was detected, not to what was weighed.''' A species that does not elute, does not absorb at the detection wavelength, or co-elutes with the principal peak contributes nothing to the denominator and therefore cannot reduce the figure. Water, counterion and inorganic residue are invisible to it in the ordinary case, which is why a vial can honestly carry a certificate reading 99.2% and contain substantially less than 99.2% peptide by mass.{{r|usp1503}} | 7 | The measure has one defining property from which everything else follows: '''it is relative to what was detected, not to what was weighed.''' A species that does not elute, does not absorb at the detection wavelength, or co-elutes with the principal peak contributes nothing to the denominator and therefore cannot reduce the figure. Water, counterion and inorganic residue are invisible to it in the ordinary case, which is why a vial can honestly carry a certificate reading 99.2% and contain substantially less than 99.2% peptide by mass.{{r|usp1503}} |
| 8 | 8 | ||
| + | 9 | == How the figure is produced == | |
| + | 10 | A sample is dissolved, injected onto a reverse-phase column, and eluted under a gradient of increasing organic modifier. A detector — most often ultraviolet absorbance at 214 nm, where the peptide bond absorbs — produces a signal against time. Peaks are integrated, and the principal peak's area is divided by the sum of all integrated areas. | |
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| + | 12 | Four choices in that description change the answer, and none of them is usually stated on a certificate: | |
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| 9 | == References == | 14 | == References == |
| 10 | {{reflist}} | 15 | {{reflist}} |