No single standard
For medicines and their ingredients, good manufacturing practice expects a certificate to list each test with its acceptance limit and result. Research-grade material is not a licensed medicine, so there is no licence specification setting its purity.
Even in medicines, peptides are a special case. The main international guideline on impurities in new drug substances, ICH Q3A(R2), says it does not cover peptides.
How certificates report purity
Most peptide certificates give a single HPLC purity figure. How precise it is depends on the lab. Janoshik, for example, reports high results in two bands: 96%+ means between 96% and 98%, and 98%+ means between 98% and 100%. It says an exact figure would need more analysis and cost more.
Janoshik also says it does not report peptide purity for blends of more than one peptide, or for capsules, because the results would not be reliable.
What a purity figure tells you
Peptide purity is the share of the peptide content that is the intact target peptide. Janoshik describes the rest as degradation products. A 98% result means about 2% of the peptide content is something else.
What it does not tell you
Educational information only. Nothing here is medical advice, dosing guidance or a recommendation to use any substance. Research peptides are not approved medicines and are not for human or animal consumption. Speak to a qualified professional and follow the law where you are.
