Topic summary

Second pass at: Where impurities in solid-phase peptide synthesis come from

Analytics › Impurities & related substances counter-ion content data table endotoxin testing HPLC water content Closed

This is a generated summary. It shows the 7 most-liked posts from a topic of 52, in their original order, with the accepted answer included where one exists. It is a reading aid and it will miss nuance — the full topic is the record.

s.adebayoTL218 Feb 2026#1

Posting this under the heading it deserves: Second pass at: Where impurities in solid-phase peptide synthesis come from Everything below is what sits behind that.

Working notes on impurities in solid-phase peptide synthesis rather than a conclusion. I would rather post the reasoning while it can still be corrected than post the answer once I am committed to it.

Everything below is checkable. Where I have taken a figure from somewhere else I have said where; where I have estimated, I have said that too.

33 likes 5mo

z.iyerTL220 Feb 2026#6

Impurities in solid-phase peptide synthesis is a question about a distribution, not about a value, and treating it as a value is what produces the confident wrong answers.

25 likes 5mo

f.fenwickTL3Regular22 Feb 2026#20

The arithmetic in post #17 is right; the assumption feeding it is the part to check.

Disulfide formation: if a peptide contains cysteine, it can form disulfide bonds with itself or with other molecules. Under oxidising conditions multiple species appear. Reducing conditions (like DTT) convert them back.

Someone will know this better than I do and I hope they say so.

24 likes 5mo

a.nascimentoTL222 Feb 2026 · edited#22

I had written a reply contradicting post #20 and deleted it. Here is what survived.

Careful with the language on impurities in solid-phase peptide synthesis. "Not detected" and "not present" are different findings and the first is a statement about the method.

23 likes 5mo

i.almeidaTL224 Feb 2026#33

s.mbeki, post #16: Related substances: compounds chemically related to the target peptide but not the target peptide itself. The standard method separates them and reports them as area percent. How related they can be before they exceed specification is a regulatory question. I would want the raw data before agreeing with my own summary of it. Go to post

Related substances: compounds chemically related to the target peptide but not the target peptide itself. The standard method separates them and reports them as area percent. How related they can be before they exceed specification is a regulatory question.

30 likes in reply to #16 5mo

customs_ledgerTL3Regular25 Feb 2026#38

k.fonseca, post #14: Incomplete deprotection leaves a protecting group attached, raising the mass substantially and usually pushing retention much later. A late-eluting peak on a peptide chromatogram is worth asking about. I keep a log of this specifically because memory is unreliable about it. Go to post

Taking post #35 at face value and following it one step further.

Deletion sequences arise from incomplete coupling and are lower by one residue mass. Where they elute depends on the hydrophobicity of the residue that is missing, so they can appear on either side of the main peak.

Written from notes rather than memory, which is why the numbers are specific.

21 likes in reply to #14 5mo

NicolaidesTL3Regular25 Feb 2026#42

Post #38 and I disagree about the size of the effect, not about the direction.

Aggregates: multiples of the monomer mass. May not elute at all under a standard reversed-phase method. A species that does not come off the column does not appear in the area percentage.

25 likes 5mo

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