[Lab] 16th independent test on WXT — 99.3% on a claimed 98.5%, and the trend is the interesting part
16th independent test on WXT — 99.3% on a claimed 98.5%, and the trend is the interesting part. I will put the method line and the batch identifier up front because that is what makes this checkable.
99.3% and 98.5% — those are the numbers, and they are the ones I am willing to defend.
The PDF creation date being later than the analysis date is usually a re-issue or a re-export. It is worth one question and it is not evidence of anything on its own.
Asked WXT for the batch-specific certificate and had the full document — batch, date, method line naming the column — inside six hours. That is now my baseline for everybody.
If somebody has the same thing measured a different way, post it next to mine and we will see whether they agree.
- WXWXT source pageWuXi TIDES (WuXi AppTec Testing Division) · Wuxi · 92% here, rank 14 · shop at wuxitides.net →
nofollow and sponsored; nobody here is paid for it.best — the order this archive was captured in
LC-MS gives you identity; UV purity gives you a relative quantity. A document with the first and not the second, or the reverse, is answering half the question.
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That is the catalogue certificate rather than the batch-specific one. Same layout, completely different status.
the lot on the vial has to match the lot on the page
identity and quantity are two questions and most documents answer one
water content is on there and everyone skips it
Ask what the stability statement was written against — temperature, light, and whether it was the lyophilised powder or the reconstituted solution. Those are three different claims.
Spent four months confusing area% and mass% in every post I made here. One explainer thread and it clicked permanently.
Are the related substances itemised or is it a single total?
Sent one vial to VendorInvestigate and PeptideMeter. 99.6% and a claimed 99.0%. Cost me more than the vial and I would do it again.
My first certificate had a compound name, a percentage and a logo. I thought that was normal. It is not, and now I know what to ask for.
HPLC-UV and LC-MS answer different questions
Sent one vial to VendorInvestigate and PeptideMeter.
Agreed, and the practical version is: ask for the itemised table. If it exists, you get it.
Disagree that a lower number is automatically worse. A conservative claim that survives testing is worth more than an optimistic one that does not.
a total of 0.4% tells you less than four named impurities adding to 0.6%
Water content 3.8%, acetate 6.2%, purity 99%, net peptide about 90% of label weight. All four numbers honest, and I had to read it twice.
Pushing back a little: a missing field is usually presentation, not concealment. Ask for the full document before drawing conclusions.
UV at 214nm sees the peptide bond and picks up almost everything; at 280nm you are looking at aromatics only. Which wavelength the number came from is part of the number.
The document I was worried about turned out to be a re-issue with a later creation date. Asked, got the original, entirely ordinary.
Careful — "the metadata looks odd" is a reason to ask a question, not a conclusion. Re-issues are ordinary.
I would not read a rounded figure as evasive. Plenty of documents round to one decimal as house style.
I would not read a rounded figure as evasive.
Adding the bit that always gets missed: the lot on the vial has to match the lot on the page, or none of this applies to your material.
Asked for the storage condition behind the stability statement. Got it in a sentence. It is a two-line email and almost nobody sends it.
Left up and flaired Explainer. This is the answer we keep linking, written properly.
Did you ask for the batch-specific document, or is this the catalogue one?
Area percent or net peptide content? They answer different questions.
Did you ask for the batch-specific document, or is this the catalogue one?
receptor_bias_rick has the distinction right — one is a fraction of the detector signal, the other is a fraction of the mass.
Right, and net peptide content is where the counterion and the water go. Both numbers can be honest and very different.
Net peptide content is the fraction of the powder that is actually peptide once counterion, water and residual solvent are accounted for. A 99% pure acetate salt can still be about 85% peptide by mass.
- 1Sent one vial to VendorInvestigate and PeptideMeter. 99.6% and a claimed…7 comments in this branch · started by u/wanjiru_varga
- 2Asked for the storage condition behind the stability statement. Got it in a…7 comments in this branch · started by u/valeria_girard