Particulates in a reconstituted solution: identifying the likely source

Posting this under the heading it deserves: Particulates in a reconstituted solution: identifying the likely source Everything below is what sits behind that.

Something about particulates does not reconcile and I would like a second pair of eyes before I decide which half is wrong.

Two sources, both reputable, giving figures that cannot both be right unless they are measuring different quantities. My suspicion is that they are, and I cannot see how.

Right — I had this wrong and I am glad to have read it before it mattered.

Picking up the opening post: that is the part I would want checked first.

Speaking only to particulates 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.

Residual solvents: traces of solvents used in purification. These are usually tested by gas chromatography, not by HPLC. A specification for residual solvents should be stated separately from the purity.

Not a conclusion. A place to stand while looking for one.

Seconded. It reads as careful rather than confident, which is the right register.

I keep a log for particulates specifically because my memory of it turned out to be systematically wrong in one direction. Six weeks of notes cost nothing and settled it.

This follows post #4 rather than contradicting it.

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 read post #6 twice before replying, because I had assumed the opposite.

Particulates is one of those subjects where the general answer and the answer for a specific case diverge, and the thread will go in circles until someone says which one is being asked for.

Post #8 answers the question as asked. The question underneath it is different.

I would rather this thread reach "we do not know" about particulates than reach a confident answer that nobody can support when asked.

The related-substances total is only as informative as the method that generated it. Two per cent by a method that resolves everything is a different statement from two per cent by a method that resolves little.

I would treat that as a working assumption and revisit it.

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.

I would not lead a decision with this, but I would not ignore it either.

Thank you for taking the time. That was more work than a reply usually is.

Trying to state the particulates position in a way that someone who disagrees would recognise as fair, because I do not think the version in this thread passes that test.

Oxidation at methionine and tryptophan: adds 16 per oxygen. Usually elutes earlier. Oxidation is common in storage, especially if the solution is exposed to light or if antioxidants are not present.