Gradient steepness and apparent purity: a worked comparison — the long version — setting out what I have, and where I think it stops being reliable.
A narrow question about Gradient steepness and apparent purity, deliberately narrow, because the broad version has been asked here four times and produced four long threads and no answer.
One question, stated units, stated method, and what I have already ruled out.
Before anything else: what was the gradient, and at what wavelength? Area percent at different wavelengths is not the same number even on the same sample because different species absorb differently at different wavelengths. With the method stated, I can tell you something useful. Without it, all I can say is that there is one large peak.
Peaks that do not elute do not appear in the area percentage. Aggregates and strongly retained species can be entirely invisible to a standard method, which is a ceiling on what any purity figure can claim.
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Second pass at: What a reversed-phase purity number actually is
On the subject in the title: Second pass at: What a reversed-phase purity number actually is Working notes rather than a conclusion. I would like to understand what this number means before I repeat it…
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2 | 7.4k | 11mo | |
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Area percent versus weight percent: the confusion that causes most arguments
Posting this under the heading it deserves: Area percent versus weight percent: the confusion that causes most arguments Everything below is what sits behind that. Proposing that area percent versus weight…
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+10 | 14 | 2.1k | 2mo |
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Why I ask for the gradient before I discuss the number
The question in the title: Why I ask for the gradient before I discuss the number I will give what I have already checked below so nobody repeats it. I would like to understand what this number means before I…
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+35 | 39 | 4.9k | 20mo |
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Coming back to: Where the integrator drew the baseline, and how much it moved the number
On the subject in the title: Where the integrator drew the baseline, and how much it moved the number Working notes rather than a conclusion. Posting the method first, because I know what the first three…
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+20 | 24 | 2.7k | 10mo |
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Shoulders, tangent skims, and defensible integration
Posting this under the heading it deserves: Shoulders, tangent skims, and defensible integration Everything below is what sits behind that. Setting out an integration problem with the actual figures, because…
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+16 | 20 | 11k | 13h |
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Revisiting: Aggregates and why a purity assay may miss them entirely
Posting this under the heading it deserves: Revisiting: Aggregates and why a purity assay may miss them entirely Everything below is what sits behind that. I would like to disagree carefully with the settled…
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+48 | 53 | 918 | 8mo |
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Shoulders, tangent skims, and defensible integration
Posting this under the heading it deserves: Shoulders, tangent skims, and defensible integration Everything below is what sits behind that. Setting out an integration problem with the actual figures, because…
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+16 | 20 | 11k | 13h |
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Resolution and tailing factor: real acceptance criteria
Resolution and tailing factor: real acceptance criteria Writing it up because I had to work it out twice and would rather nobody else did. Asking about resolution and tailing factor on behalf of the question…
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[2026 update] Detection wavelength and why 214 nm and 280 nm disagree
Detection wavelength and why 214 nm and 280 nm disagree — setting out what I have, and where I think it stops being reliable. I would like to disagree carefully with the settled view on Detection wavelength,…
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+69 | 76 | 920 | 6h |
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Validating a method you did not develop
On the subject in the title: Validating a method you did not develop Working notes rather than a conclusion. What changes if the standard account of validating a method is wrong? I ask because I have been…
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+10 | 14 | 15k | 3mo |