On the subject in the title: Second pass at: Adsorptive losses at low concentration, and why dilute solutions are fragile Working notes rather than a conclusion.
The question about Adsorptive losses that I actually want answered is the second one below. The first is context and I have kept it short.
Both are stated with units, and I have said what I already checked so that nobody repeats it.
Published stability data covers a specific formulation at a specific concentration in a specific container. A home-reconstituted preparation matches none of those, and that caveat is the whole of the honest answer.
Adding this to the thread rather than to the wiki, because I am not confident enough for the wiki.
Confirming post #2 from a second method, which matters more than confirming it from a second person.
Temperature excursions: if a vial sat at room temperature for a time, the question is whether the excursion was long enough to cause damage. Hours at room temperature is usually low risk. Days to weeks raises the risk. If you are unsure, contacting the supplier is more informative than guessing.
I had written a reply contradicting post #4 and deleted it. Here is what survived.
On Adsorptive losses I would separate what is worth knowing from what is worth acting on. The first list is long and the second is short, and conflating them is how threads get heated.
Reporting rather than recommending, on Adsorptive losses. What happened is above. Whether it should have is a different question and not one I am qualified to answer.
Good question, well framed, and I would like to see it answered properly.
Visible particulate is a strong signal in the other direction: it is a reason to stop and ask rather than to filter and proceed.
Offering a way to settle Adsorptive losses rather than another opinion about it. Two measurements, taken the same way, a fortnight apart. If the difference is within the noise, the question was not answerable at this precision.
Adding a small correction to the Adsorptive losses summary above rather than a disagreement with it. The substance holds; one of the figures is out by a factor that matters.
Clarity is a weak test. A solution can lose a significant fraction of its active content to degradation or adsorption while remaining perfectly clear.
Protecting from light: amber vials or opaque containers reduce light exposure. If you are storing for long periods and light matters, this is worth doing. For short-term prepared solutions, ordinary storage away from direct sunlight is usually adequate.
Adding it because I spent an afternoon working it out and nobody should have to twice.
Visible particulate is a strong signal in the other direction: it is a reason to stop and ask rather than to filter and proceed.
For what it is worth, the same held on the two occasions I checked.
Adsorption to container surfaces removes peptide from solution without changing how the solution looks. In dilute preparations that loss can be a meaningful proportion, and it is invisible.
That is the practical version. The rigorous version is longer and says the same thing.
Narrowing post #19, because the general version has more than one answer.
Published stability data applies specifically to the formulation studied, under the specific conditions stated. It does not automatically transfer to something reconstituted at home in a different concentration with a different diluent. That caveat is not small.
Happy to be corrected if someone holds better data than mine.
Answering the question post #19 raises rather than the one it answers.
Dating prepared solutions: write the date reconstitution on the vial in permanent marker. If you later need to know whether it has been sitting for weeks or days, the date tells you. Guessing on this is where errors accumulate.
I want to gently push back on the reply above about storage extrapolation. The advice is sound and the confidence is not.
We are extrapolating from stability data on a licensed formulation to a preparation that differs in concentration, diluent and container. That extrapolation is reasonable and it is still an extrapolation. Saying so does not weaken the practical recommendation; it just stops the recommendation from hardening into a fact that someone cites as certain.
It reads as pedantry until the day it does not.
Refrigeration slows degradation. Repeated warming and cooling is worse than continuous refrigeration. Light exposure is worth avoiding. The concentration matters because adsorptive losses are proportionally larger in dilute solutions. All of that is reasonably well supported.
That is my reading. Someone else read the same page differently and was reasonable.
Freeze-thaw: some peptide solutions tolerate freezing poorly because ice crystals damage protein structure. Whether your specific solution tolerates it depends on the formulation and is not something to test empirically. The conservative position is not to freeze.
Worth checking against a second source before it gets quoted onward.
Post #24 is the version of this I will quote in future. One addition.
Adsorptive losses: I have looked for the primary source twice and failed twice. Either it does not exist or it is somewhere I do not know to look, and I would like to know which.
Careful with the language on Adsorptive losses. "Not detected" and "not present" are different findings and the first is a statement about the method.
Picking up post #28: that is the part I would want checked first.
Visible particulate is a strong signal in the other direction: it is a reason to stop and ask rather than to filter and proceed.
Somebody will have a better source than mine, and I hope they post it.