Regulatory reference
What a certificate of analysis can and cannot establish.
Written by Eric W. Anderson, MD · Last updated
A certificate of analysis is the most technical-looking document in this space, which is exactly why it is over-read. It reports specific measurements on a specific sample. Understanding its boundaries is more useful than learning to admire it.
What the document reports
A typical peptide certificate contains four kinds of information, and each has a narrow meaning.
- HPLC purity. The sample is separated by high-performance liquid chromatography and the target peak is expressed as a percentage of total detected peptide-related material. It is a relative measure within the peptide fraction.
- Mass spectrometry identity. The observed molecular mass is compared with the theoretical mass of the target sequence. This confirms that the principal species is consistent with the intended molecule.
- Net peptide content. The proportion of the dry mass that is peptide rather than water, salts or counter-ions. Often reported; often ignored.
- Water and counter-ion content. Residual moisture and the acetate or trifluoroacetate left from synthesis and purification. Together these account for most of the gap between gross weight and peptide weight.
Purity is not peptide content
This is the distinction almost nobody explains, and it is the most consequential thing on the page. Purity and net peptide content answer different questions, and a high figure on one says nothing about the other.
Purity asks: of the peptide material present, what fraction is the right peptide? Net peptide content asks: of the powder in the vial, what fraction is peptide at all?
Worked example
A vial is labeled 10 mg. The certificate reports 99% HPLC purity and 70% net peptide content.
Peptide mass = 10 mg × 0.70 = 7 mg. Of that 7 mg, 99% is the target sequence: about 6.93 mg of the intended molecule.
Someone reading only the purity figure believes they are working with roughly 10 mg. The actual quantity of active substance is about 31% lower. If that same person calculates a dose from the label weight, every dose is off by that margin — and if the next vial reports 85% net peptide content, the same arithmetic silently produces a 21% different dose.
Nothing about this is exotic; it is standard peptide chemistry. It is simply invisible to anyone who reads the large percentage at the top of the document and stops there.
What a certificate does not cover
- Sterility. Not tested, not implied, not addressed. A purity assay says nothing about viable organisms.
- Endotoxin. Bacterial pyrogens survive processes that kill bacteria, and detecting them requires a separate assay that is rarely supplied.
- Stability over time. The document describes the sample on the day it was tested — not after months of storage, temperature excursion in transit, or reconstitution.
- Whether the tested lot is the lot in the vial. A certificate describes a sample. Linking that sample to a specific unit requires lot traceability that this category does not provide.
The verification gap
Set aside outright forgery, which is possible but not the main issue. The structural problem is that the document is supplied by the party selling the material, describing a sample that party selected.
Frequently there is no independent laboratory named, no analyst or instrument identifier, no date that can be checked against a batch record, and no lot number that a purchaser could trace to the vial received. Even taken entirely at face value, a certificate in those circumstances establishes a fact about a sample of material, somewhere, at some point.
Compare that with lot release in a licensed pharmacy, where the tested batch, the release record and the dispensed unit are the same traceable object. The difference is not the quality of the chemistry. It is whether the document is connected to your vial.
A manufacturing document, not a safety finding
A certificate of analysis is a manufacturing quality record. It was designed to communicate analytical results between parties who already operate inside a quality system.
No reading of one converts it into a determination that a material is appropriate or safe for use in a person. That determination requires sterility and endotoxin data on the finished preparation, an established chain of custody, and a clinician evaluating the person rather than the powder. A certificate contributes to none of those.
Frequently asked questions.
- What does 99% purity actually mean?
- It usually means that in an HPLC chromatogram of the tested sample, 99% of the detected peptide-related material eluted as the target peak. It is a statement about the relative proportion of peptide species in that sample — not about how much peptide is in the vial, and not about anything non-peptide such as water, salts or residual solvent.
- What is net peptide content?
- Net peptide content is the fraction of the dry powder's mass that is actually peptide, as opposed to bound water and counter-ions such as acetate or trifluoroacetate. It is commonly 70–85%. A vial labeled 10 mg at 80% net peptide content holds roughly 8 mg of peptide, even at 99% purity.
- Does a CoA prove a product is sterile?
- No. Sterility is established by a separate test on the finished preparation, and endotoxin by another test again. A purity and identity certificate speaks to neither, and a document that does not report a sterility result is not evidence of sterility.
- Can a CoA be faked?
- A certificate is a document, and documents can be copied, edited or reused across batches. The more fundamental problem is structural rather than fraudulent: even a genuine certificate describes a sample submitted by the party selling the material, frequently with no independent laboratory identifier and no lot number that ties it to the vial in your hand.
Related reading
What purity doesn't tell you
Purity, sterility and pyrogen-free are three properties measured by three different tests.
What research-use-only actually means
Why no document in this category carries an enforceable standard behind it.
Research-use-only vs. prescribed
Lot release, verification and recall — the mechanisms a certificate cannot substitute for.
Educational content only. This page is not medical advice, not a diagnosis, and not an offer to sell any product.