Three numbers, three questions
A certificate of analysis (COA) for a research peptide usually reports several values, and they answer different questions. Confusing them is the most common mistake buyers make.
Chromatographic purity (HPLC %) answers "what fraction of the peptide-related material is the target peptide?" It is measured by high-performance liquid chromatography, which separates the main peptide from related impurities. Independent labs such as Janoshik Analytical report this as a percentage — for research-grade material, values in the high-90s are commonly cited as good.
Net peptide content answers a different question: "of the powder in the vial, how much is actually peptide?" The remainder is water, counter-ions (often acetate or trifluoroacetate), and salts left from synthesis. A vial can be 99% *pure* by HPLC yet contain noticeably less than its labeled mass in actual peptide, because purity and content are independent measurements.
Identity answers "is this the right molecule at all?" It is confirmed by mass spectrometry, which checks molecular weight against the expected value. Purity is meaningless if the identity is wrong.
What a grade does and doesn't tell you
Aggregated grades — such as the A–E ratings published by Finnrick, which we cite on our vendor pages with attribution — roll these measurements, plus dose accuracy, into a single letter. That is useful for scanning, but the underlying COA is where the detail lives. A grade is a summary of someone else's testing, not a substitute for reading the report.
Reading the report itself
A few things worth checking, drawn from how analytical labs describe their own methods:
- Who ran the test. A COA hosted on an independent lab's own domain is more verifiable than a PDF or screenshot supplied by the seller. Janoshik, for example, lets buyers verify a report by its reference number.
- The date and batch. Testing applies to the batch tested. A COA from a different batch is evidence about a different production run.
- The method. HPLC purity and MS identity should both be present; a purity number with no identity confirmation is incomplete.
We aggregate and link these reports rather than re-grade them ourselves — the goal is to make the original testing easy to find and read, not to replace it.