Coming back to: Reconciling a supplier certificate with an independent result

Posting this under the heading it deserves: Reconciling a supplier certificate with an independent result Everything below is what sits behind that.

Structured report rather than an opinion, following the format the maintainers asked for.

• Compound: tirzepatide
• Independent testing: Medutest
• Method as reported: reversed-phase HPLC, 214 nm
• Result: 98.3% area
• Certificate figure for the same lot: 98.1%

I am not drawing a conclusion about the supplier from one lot and I would ask that nobody else does either. I am adding a data point to a record.

Date the report: when the analysis was done matters. Material can degrade in storage. A report from two years ago is still useful but is not evidence about the current state of the same supplier's stock.

For anyone arriving from a search: the marked solution above is the direct answer, and the replies underneath it add the caveats that make it safe to use.

Coming back to post #3, because the follow-up matters more than the original answer.

Disputed records: when a result disagreed and was not explained, the record says disputed and stays that way. We do not remove inconvenient history; we document it.

post #4 is right about the mechanism and I think understates the practical bit.

Temporal patterns: if results from a supplier were good two years ago but have deteriorated recently, that is information. If they have been consistent over years, that is also information.

Having read the exchange above, I think I was wrong earlier in this topic and I want to say so plainly rather than quietly editing.

The correction was fair and I had been repeating something I had not checked carefully enough.

Blind submission is worth the effort: have someone else relabel the sample so neither you nor the laboratory knows which supplier it came from until the result is back. Blind results change minds; self-selected results do not.

Structured report format: compound, lot, independent testing service, method as reported, result, and the certificate figure for the same lot. One lot is one lot. It becomes a pattern at three or four, and it becomes a disputed record when asked and not explained.

Testing service selection: Janoshik gives purity with chromatogram. Medutest gives combined purity and identity. PeptideMeter gives verification records as well as results. VendorInvestigate reviews documentation. They answer different questions.

On post #6 — agreed on the reasoning, with one qualification.

Lot matching: confirm the lot number on the certificate matches the lot number on the vial. A result from a different lot is not evidence about your vial.

Coming back to post #9, because the follow-up matters more than the original answer.

Multiple services on one lot: agreement across two independent laboratories is stronger than a high number from one. Our vendor pages deliberately mix services for that reason.

Dosing and purity: a vial that is 99% pure might contain 80% of its label claim if the other mass is water, counter-ion, and excipient. Purity and content are different. Both matter for different reasons.

Pattern across lots: a single result is a data point. Three or four results from the same supplier showing a consistent pattern becomes a record worth discussing. Two results that disagree might just be measurement variation.

post #13 answers the question as asked. The question underneath it is different.

For anyone arriving from a search: the marked solution above is the direct answer, and the replies underneath it add the caveats that make it safe to use.