Trifluoroacetate content and its consequences

Trifluoroacetate content and its consequences — setting out what I have, and where I think it stops being reliable.

A documentation question rather than an analytical one.

I have a certificate in front of me that reports a purity figure, names a technique, gives a wavelength, and stops. No gradient, no column, no injection volume, no chromatogram.

What can I legitimately conclude from that document? My instinct is "almost nothing, but not literally nothing", and I would like to know where the people who read these professionally draw the line.

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.

Incomplete deprotection: mass higher by the protecting group mass. Usually markedly later eluting. A synthesis artifact from incomplete removal of protecting groups.

Coming back to post #27, because the follow-up matters more than the original answer.

Practical note that does not fit anywhere else. Whatever you conclude from this topic, write down what you did and when. The single most useful thing in your own records is not any individual result; it is that they are dated and consecutive.

On post #32 — agreed on the reasoning, with one qualification.

Deletion sequences (incomplete coupling during synthesis): lower in mass by one residue. Chromatographically they usually elute earlier or later depending on the residue's hydrophobicity. They are the most common impurity in solid-phase synthesis.

Worth separating two things that post #45 runs together.

Deletion sequences (incomplete coupling during synthesis): lower in mass by one residue. Chromatographically they usually elute earlier or later depending on the residue's hydrophobicity. They are the most common impurity in solid-phase synthesis.

post #74 is right about the mechanism and I think understates the practical bit.

Truncation products: fragments from incomplete synthesis or from degradation. They elute quite differently from the intact peptide because they are much smaller and have different hydrophobicity. They are usually well separated.

Incomplete deprotection: mass higher by the protecting group mass. Usually markedly later eluting. A synthesis artifact from incomplete removal of protecting groups.

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.