Revisiting: Aggregate verification data across the directory, with caveats

Revisiting: Aggregate verification data across the directory, with caveats — setting out what I have, and where I think it stops being reliable.

I would like to talk about documentation quality as a signal, separately from product quality.

Across the certificates I have collected, the variation in what is disclosed is much larger than the variation in the purity figures. Some name the analytical procedure; some give a number and a signature.

My hypothesis is that disclosure correlates with process control, and I would like to know whether the people who audit paperwork for a living think that is naive.

Thank you for the correction. I have edited my earlier post with a note rather than silently, so the thread still makes sense to read. The error was mine and it was the kind that comes from remembering a figure instead of looking it up.

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.

post #2 answers the question as asked. The question underneath it is different.

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.

I read post #3 twice before replying, because I had assumed the opposite.

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.

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.

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.

Coming back to post #7, because the follow-up matters more than the original answer.

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.

Picking up post #8: that is the part I would want checked first.

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.

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.

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.