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?

A question about how a record should be read rather than about a supplier.

We have results from VendorInvestigate and from Janoshik on the same product line, months apart, agreeing closely. My question is what that agreement actually establishes, given that neither saw the other's sample.

I suspect the honest answer is narrower than it feels, and I would like it stated precisely.

I would keep Janoshik and the decision it usually gets used for separate in this thread. They are related and they are not the same question, and merging them is why the last one went badly.

Building on post #2 rather than restating it.

The record shows what was measured. Everything beyond that is inference and this site tries to keep the line visible.

A partial answer, offered because a partial answer beats none.

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.

Posted with less confidence than the sentence structure implies.

It does not extend to lots nobody has seen, it is not a recommendation, and it says nothing about anything other than what was measured.

Two sources, same conclusion, and I could not rule out that one copied the other.

Careful with the language on Janoshik. "Not detected" and "not present" are different findings and the first is a statement about the method.

Taking post #6 at face value and following it one step further.

Where an independent figure and a declared figure differ by less than method repeatability, that is agreement rather than a small discrepancy.

This is the sort of thing that ought to be settled and apparently is not.

Post #4 and I disagree about the size of the effect, not about the direction.

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.

This is the sort of thing the wiki should carry and currently does not.

Adding the measurement that post #6 says would settle it.

Trying to state the Janoshik 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.

Post #8 describes the usual case. This is about the unusual one.

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.

Adding this to the thread rather than to the wiki, because I am not confident enough for the wiki.

Second-hand on Janoshik, so weight it accordingly — someone whose method I trust told me this and I have not verified it myself.

Post #11 is the version of this I will quote in future. One addition.

Offering a way to settle Janoshik 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.

Answering the question post #11 raises rather than the one it answers.

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.

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.

If this contradicts something upthread, the upthread version may well be the better one.