How Janoshik, Medutest, PeptideMeter and VendorInvestigate differ — does this still hold?

Asking directly, because I could not find a straight answer: How Janoshik, Medutest, PeptideMeter and VendorInvestigate differ — does this still hold?

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

• Compound: semaglutide
• Independent testing: VendorInvestigate
• Method as reported: reversed-phase HPLC, 280 nm
• Result: 96.5% area
• Certificate figure for the same lot: 98.8%

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.

How to submit a sample: contact the service directly. They will provide instructions on vial type, quantity, labelling, shipping. Following their instructions exactly ensures results are interpretable.

post #2 is right about the mechanism and I think understates the practical bit.

Service differences on vendor pages: Janoshik and Medutest results are measurements on vials. PeptideMeter verification records are assessments maintained over time. VendorInvestigate reviews are documentation assessments. We cite all four because they answer different questions.

Blind sampling: submitting without the laboratory or seller knowing the source removes the two easiest ways for a result to be shaped: selective submission and selective reporting. The extra effort is worth it.

VendorInvestigate: documentation and supplier-practice review. Reviews paperwork rather than vials. Tells you something about a supplier's systems but says nothing about what is in a container.

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.

post #6 answers the question as asked. The question underneath it is different.

Medutest: combined purity and identity reporting. Appears throughout vendor documentation. Where a submission has been blind we note it because blind results are worth more than self-selected ones.

On post #4 — agreed on the reasoning, with one qualification.

Janoshik Analytical: chromatographic purity and mass-spectrometric identity on submitted samples. Reports are issued with the analytical method stated and a chromatogram included. Submission is by mail.

This follows post #6 rather than contradicting it.

Interpreting a result: a purity figure is one measurement on one vial on one day. Agreement across two services is much stronger. A single high number does not establish a pattern.

I read post #8 twice before replying, because I had assumed the opposite.

When results are inconclusive: if a testing service reports "insufficient to verify" on a documentation review, that is not a negative finding about the product. It means the documents did not contain enough to check.

Repeat testing: if you want to verify the same lot a second time, testing with a different service strengthens the conclusion. Testing with the same service verifies reproducibility but uses the same method.

post #11 is right about the mechanism and I think understates the practical bit.

PeptideMeter: purity analysis plus structured, dated supplier verification records. Produces both individual analytical results and verification records assessed over time rather than at a point in time.

I read post #11 twice before replying, because I had assumed the opposite.

Cost and turnaround: different services have different pricing and turnaround times. Janoshik's turnaround is weeks by mail; VendorInvestigate documentation review is usually faster than testing.

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.