roxy_nash said:

My vendor review relevant to certificates of analysis: ordered 5 times from my current compounder.

My HPLC chromatogram analysis for certificates of analysis — I sent my batch to Janoshik and here's what the results showed:

Main peak retention time: 15.3 minutes (consistent with semaglutide reference standard)
Peak purity: 99.4%
Related substances: 0.4% (single impurity at 9.7 minutes — likely a synthesis intermediate)
Mass spec: m/z 4113.6 (matches expected molecular weight)

This is a clean result. The mass spec confirmation is particularly important — it proves the molecule is actually semaglutide and not a substitution.

Adding the numbers, since they settle part of this. For anyone reading later: the numbers in this thread are worth checking against a primary source before you act on them, including mine. Half the figures circulating in this community trace back to a secondary summary that dropped a qualifier.

I would rather be corrected than agreed with, if it comes to it.

Following on from roxy_nash — and this may be the naive question:

Was that from a primary source or from a summary of one?

hank_denver said:

For anyone reading later: the numbers in this thread are worth checking against a primary source before you act on them, including mine.

This is where I part company with the consensus forming above. The objection nobody has made: this only works if the measurement is doing what we assume it is doing, and that assumption has not been tested here.

hank_denver said:

For anyone reading later: the numbers in this thread are worth checking against a primary source before you act on them, including mine.

That is right for the common case. Whether it is right for the case being asked about depends on a detail that has not been given.