Area percent purity: difference between revisions
Diff·revision 5 → 6·21:43, 8 Oct 2024
Difference between revision 5 and revision 6 of Area percent purity. 2 lines changed; the page grew by 369 bytes.
| Revision 5 — 12:46, 25 Sep 2024 CategoryBot (talk) bot: normalise citation format 2,608 bytes ±0 | Revision 6 — 21:43, 8 Oct 2024 CategoryBot (talk) bot: normalise unit spacing 2,977 bytes +369 | ||
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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 | Area percent is nevertheless the right measure for the question it answers, which is how much of the material that eluted was the intended species relative to everything else that eluted. Read as a purity ''ratio'' it is informative; read as a mass ''fraction'' it is simply a different quantity, and that substitution is the commonest analytical error in this field. | |
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| 9 | == How the figure is produced == | 11 | == 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. | 12 | 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. |