Sterility testing per USP <71> — need advice

Short answer first, then the reasoning. They are not contradictory, they measure different things, and this is the single most common misreading of a certificate. Purity is a relative area measurement: the main peak as a percentage of total peak area in the chromatogram. Content is an absolute mass measurement against a reference standard. A vial can be 99% pure and contain 6.1mg — pure material, overfilled — or 99% pure and contain 3mg, which is pure material and a short fill. Purity tells you what fraction of what is there is the right molecule; content tells you how much of it there is. You need both, and a certificate with only purity is telling you half the story.

pete_manc_UK said:

They are not contradictory, they measure different things, and this is the single most common misreading of a certificate.

pete_manc_UK has the substance of this right. The condition it depends on is worth stating. One addition: an unstated method makes a report close to uninterpretable. "99% pure" without the technique, the standard and the conditions is a claim, not a measurement.

sarah_TO said:

I have a certificate reporting 99.2% purity and 6.1mg content on a vial sold as 5mg, and I cannot work out whether those two numbers are consistent or…

Same position here, arrived at the long way round. The provenance questions are more useful than the numbers. Does the report name the batch on your vial. Is the date consistent with when that batch existed. Is it addressed to the vendor or to the person who paid for the test. Was the sample taken from general stock or supplied by the vendor. A perfect certificate for a different batch is worth nothing, and vendor-supplied samples are the most common way a genuine report ends up misleading.

Ask again with the specifics and you will get a better answer than this one.

From the other side of the consultation, briefly.

Third-party testing services for certificates of analysis besides Janoshik:

• Janoshik: Gold standard for peptide community, ~$122, 10-14 day turnaround
• Valitech: US-based, ISO 17025 accredited, ~$222
• Eurofins: Full pharmaceutical testing suite, more expensive but comprehensive
• ChemTox: Basic identity and purity testing, ~$122

Janoshik is the community standard but any ISO-accredited analytical lab can verify peptide identity and purity. The key is independence — don't rely solely on the vendor's own testing.