Aggregates and why a purity assay may miss them entirely posts 61–70
This is a continuation of a long topic, addressed by post number rather than by page. Start at post 1.
A supplier that can tell you what its principal impurity is has answered a harder question than one that can tell you its purity, and the answer is more useful.
Worth separating two things that post #62 runs together.
The useful distinction on aggregates is between what was measured and what was inferred from it. Both end up in the same sentence and only one of them has error bars.
This follows post #62 rather than contradicting it.
Speaking only to aggregates as I have actually seen it, rather than as it is usually described: the effect is real, it is smaller than the thread suggests, and the variance between people is larger than the effect.
Aggregates may be a multiple of the monomer mass and may not elute at all under a standard method. What does not come off the column does not appear in the area percentage.
That is my reading. Someone else read the same page differently and was reasonable.
Dimer and higher-order multimers: two or more peptide molecules bonded together. They appear at double the mass and higher. They may or may not separate from the monomer on HPLC depending on the method.
I would want a second opinion before relying on that.
Picking up post #65: that is the part I would want checked first.
Source for the aggregates figure, since it was asked for. It is in the discussion rather than the abstract, which is why the version circulating is stronger than the paper is.
Reading the surrounding paragraph is worth the two minutes. The authors are more careful than their summarisers.
I had written a reply contradicting post #65 and deleted it. Here is what survived.
Acetate content: counter-ion content. Trifluoroacetate or acetate from the salt form of the peptide. Affects mass calculations and should be stated on a complete certificate.
I am describing what is, rather than arguing for what should be.
This topic was referenced in
- Residual solvents and scavengers: what is looked for — what changed sinceAnalytics › Impurities & related substances · 41 replies
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