A Certificate of Analysis is the document most researchers reach for first when evaluating a peptide lot, but it is not one test. It is a bundle of several independent measurements, run by different instruments, each answering a narrow question. Treating the whole page as a single pass/fail grade is the most common way a CoA gets misread. This walkthrough goes field by field: what each number measures, what method produces it, and — just as important — what it does not establish.

Product and lot identification

Before any test result, a usable CoA identifies exactly what was tested: product name, lot or batch number, vial fill weight, and the date of manufacture and date of testing. This block is what lets you tie a physical vial on your bench to a specific record. If the lot number on the CoA doesn’t match the lot number printed on the vial label, the document in front of you is not evidence for the vial in front of you — full stop, regardless of how clean the rest of the page looks.

The HPLC purity trace

Reversed-phase HPLC separates a sample by hydrophobicity and reports the area under the main peak as a percentage of the total chromatogram area. A trace reading ≥98% purity means less than 2% of the detected signal (by area, not necessarily by mass) falls outside the main peak’s retention time. That is a real, checkable measurement — but it is reported in area-percent, and area-percent is not automatically the same as weight-percent. Area-% assumes every co-eluting species absorbs UV light at the same wavelength with the same efficiency as your target peptide, which is not always true. It also says nothing about what the peptide is — only that most of the sample elutes at one retention time.

Mass spec identity confirmation

Identity is a separate test from purity, and a rigorous CoA reports it separately. LC-MS or MALDI-TOF measures the observed molecular mass and compares it to the theoretical mass calculated from the peptide’s sequence. A match within a stated tolerance (commonly ≤10 ppm on high-resolution instruments, wider on lower-resolution ones) confirms that the dominant species has the right mass for the sequence ordered. It does not confirm biological activity, and it can miss problems that don’t change mass — a wrong disulfide bridge pairing, for instance, is invisible to both HPLC retention time and MS mass, because the isomer is chemically identical in both respects.

Appearance and testing method disclosure

Two smaller fields are easy to skip but worth reading: appearance and method disclosure. Appearance is usually a short physical description — “white to off-white lyophilized powder,” for instance — and it exists as a sanity check, not a test result. It lets you compare what arrived against what the record describes before you touch any of the analytical numbers; a vial that looks visibly wrong relative to its own CoA is worth flagging before it goes into a freezer, regardless of how clean the purity trace reads. Method disclosure is the finer-grained field: which HPLC column and detection wavelength produced the purity trace, and which instrument (LC-MS vs. MALDI-TOF, and at what resolution) produced the mass result. A CoA that names its methods lets you judge how much confidence a given tolerance actually buys you; a CoA that reports only a bare percentage with no method behind it is harder to evaluate on its own terms.

Water content and net peptide content

This is the field most often skipped by readers, and it’s usually the one that explains a gap between the vial’s labeled weight and what a downstream assay expects. Karl Fischer titration reports residual water content in the lyophilized powder — typically a few percent by mass for a well-dried lot. Net peptide content goes further: it corrects the gross powder weight for water, residual counter-ions (commonly acetate or trifluoroacetate salts left over from HPLC purification), and other non-peptide mass, to state what fraction of the vial is actually peptide chain. A vial can carry a clean 99% HPLC purity trace and still have a net peptide content in the 70–85% range once salt and water are subtracted. Both numbers are correct; they are answering different questions, and a CoA that reports only HPLC purity is silent on the second one.

What a CoA does not tell you

A CoA is a snapshot from the testing lab, at the time of testing, on the tests actually run. Reading a clean report as proof of anything beyond that is where interpretation goes wrong. Specifically, a standard purity/identity CoA does not establish:

  • Biological or receptor activity. Purity and identity are necessary for a compound to behave as expected in an assay; they are not sufficient. Activity is a separate, assay-specific measurement no CoA vendor can run for you.
  • Sterility or bioburden, unless the CoA explicitly reports a sterility or endotoxin test. “Research-grade” and “sterile” are different claims resting on different test methods; absence of a sterility line item means the claim was not tested, not that it was confirmed.
  • Stability after the test date. HPLC purity measured at manufacture says nothing about the state of the lot after transit, after time on a shelf, or after a storage excursion. That is a handling question, not a CoA question.
  • Anything about a different lot. CoAs are lot-specific by design. A CoA for lot A is not evidence for lot B, even of the identical product, from the identical supplier.

Why a specification sheet is not a CoA

It’s worth distinguishing a Certificate of Analysis from a specification sheet, since the two look similar but claim different things. A specification sheet describes what a product line is expected to measure — typical purity range, expected mass, general appearance — and it applies, in principle, to every lot of that product ever made. A CoA reports what a specific, identified lot actually measured when it was tested. A supplier that substitutes a specification sheet for a CoA is telling you what the product is supposed to look like, not what your vial tested at. The lot number is what tells the two apart at a glance: a genuine CoA names one, a specification sheet does not.

Reading a live example

The clearest way to see these fields in context is against a real document. Vitatide’s COA library publishes the lot-specific certificates behind live inventory, including BPC-157, GHK-Cu, and Retatrutide, where testing-lab purity and identity results are posted alongside the product page rather than held back until requested. Before relying on any CoA — Vitatide’s or otherwise — work through the same short sequence: confirm the lot number on the document matches the lot number on the vial, identify which of the fields above the document actually reports (purity, identity, water content, net peptide content, sterility), and note which it omits. A document that’s silent on a field isn’t evidence the underlying property is fine — it’s evidence the test wasn’t run, and treating the two as equivalent is the gap this walkthrough exists to close.

For laboratory research use only. Not for human consumption, diagnostic, or therapeutic use.