Endotoxin and why it is a separate question from purity Writing it up because I had to work it out twice and would rather nobody else did.
A question about endotoxin that I think has a definite answer, unlike most of what I ask here.
I have the reasoning below and I am fairly confident about the direction. I am not confident about the size, and the size is what the decision turns on.
The honest reading of a purity figure: it is an upper bound on how much of what the method could see was the intended species, under one integration convention, on one sample.
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Follow-up: Trifluoroacetate content and its consequences
On the subject in the title: Trifluoroacetate content and its consequences Working notes rather than a conclusion. A follow-up question about Trifluoroacetate content that I did not know to ask the first…
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+12 | 16 | 5.7k | 21mo |
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Racemisation and why it is invisible to a mass measurement
Posting this under the heading it deserves: Racemisation and why it is invisible to a mass measurement Everything below is what sits behind that. A question about racemisation that I think has a definite…
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+120 | 127 | 41k | 1mo |
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Deamidation and the close-eluting pair it produces
Deamidation and the close-eluting pair it produces Writing it up because I had to work it out twice and would rather nobody else did. Something about deamidation does not reconcile and I would like a second…
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+33 | 37 | 46k | 15mo |
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Particulates in a reconstituted solution: identifying the likely source — what changed since
Particulates in a reconstituted solution: identifying the likely source — what changed since — setting out what I have, and where I think it stops being reliable. What changes if the standard account of…
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2 | 129 | 14mo | |
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Deletion sequences: expected mass shifts by residue
Deletion sequences: expected mass shifts by residue — setting out what I have, and where I think it stops being reliable. Deletion sequences keeps being re-asked here and I think that is because the answer is…
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2 | 59 | 3mo |
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Oxidation pathways for methionine and tryptophan
Posting this under the heading it deserves: Oxidation pathways for methionine and tryptophan Everything below is what sits behind that. Working notes on oxidation pathways for methionine rather than a…
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+58 | 63 | 1k | 19mo |
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[2026 update] Why mass spectrometry cannot tell you about an epimer
Why mass spectrometry cannot tell you about an epimer — that is the question, and I have not found it answered plainly anywhere I have looked. Working through the identity arithmetic and I would like it…
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2 | 1k | 8mo | |
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Second pass at: Where impurities in solid-phase peptide synthesis come from
Second pass at: Where impurities in solid-phase peptide synthesis come from Writing it up because I had to work it out twice and would rather nobody else did. Impurities in solid-phase peptide synthesis, from…
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+4 | 8 | 7.2k | 1mo |
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[2026 update] A rising related-substance total over six months: degradation or method drift?
The question in the title: A rising related-substance total over six months: degradation or method drift? I will give what I have already checked below so nobody repeats it. Posting the method first, because…
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+71 | 78 | 34k | 5mo |
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Second pass at: Buffers, pH and why a formulation is a formulation
Second pass at: Buffers, pH and why a formulation is a formulation Writing it up because I had to work it out twice and would rather nobody else did. Posting a small dataset on Buffers. It is mine, it is…
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+24 | 28 | 1.5k | 21mo |