Does "99 % purity" on the CoA mean the product is safe and genuine?

No. First, HPLC purity is only an estimate (area percent), under which impurities can hide. Second, purity says nothing about identity: 99 % pure can mean 99 % of the wrong peptide. Without mass spectrometry and - for injectables - sterility and endotoxin testing, "99 %" is worth little.

What is the difference between purity and net peptide content?

Purity (by HPLC) describes what proportion of the detected substance is the target substance. The net peptide content describes what proportion of the total powder mass is actually peptide - the rest is salts, counterions, and water. These are two different figures that a good CoA reports separately.

Can you trust a CoA from the seller?

Only with caution. A certificate produced by the supplier itself or circulated as a mere image file, without an independent third-party laboratory, without a batch number, and without proof of identity or sterility, is not a reliable piece of evidence. Independent analyses have repeatedly found large deviations from the certificate figures in gray-market goods.

Safety & Quality9 min readLast reviewed: June 2026

Reading a Certificate of Analysis (CoA) and HPLC purity correctly

Anyone who looks into peptides quickly comes across "certificates of analysis" (CoA) and purity figures such as "99 % HPLC". These documents look reputable - but a CoA is only worth as much as what it says and who produced it. This article explains what a CoA should contain, what an HPLC purity of "99 %" really says (and what it does not), and how to recognize useless or forged gray-market certificates. This is explicitly not about sources of supply or usage, but about critical reading skills and quality awareness.

Machine-assisted translation. The German original is the authoritative version.

Key points

A CoA is batch-specific and should contain identity, batch number, method, measured values, specification, date, and testing laboratory - numbers rather than just "passed".
HPLC purity is an area-percent estimate: it says how much of the main substance is present, not what it is.
Purity is not identity: only mass spectrometry proves that it is the right peptide. Good quality control combines HPLC and MS.
Net peptide content, sterility, and endotoxin testing are separate, important entries - especially for injectable products.
Gray-market CoAs are often unreliable or forged; independent analyses found purities of only ~8-14 % in over-the-counter online semaglutide.

What a Certificate of Analysis (CoA) is - and what it must contain

A certificate of analysis is a batch-specific quality document: it describes the test results for exactly one production batch. A meaningful CoA names at minimum: the product or identity designation, a batch or lot number (traceable to manufacturing), the test methods used (with method specification), the actual measurement results as numerical values - not just "passed" -, alongside the respective specification (acceptance limit), the manufacturing or testing date, and the testing laboratory with a signature.

Rule of thumb when reading: each measured value should appear directly next to its specification, so that you can judge for yourself whether it was met. A "passed" without a concrete figure is a weak certificate.

A CoA always applies to a specific batch (batch number).
Mandatory entries: identity, batch, method, measured value, specification, date, laboratory.
Measured values as numbers - not just "passed / failed".
Values and specification should appear side by side.

HPLC purity: what the percentage measures - and what it does not

The most common figure is "purity by HPLC". HPLC (high-performance liquid chromatography) separates the components of a sample; the purity is calculated as area percent: area of the target signal divided by the total area of all signals. This is an estimate, not an absolute value - impurities that come off the separation column at the same time (co-elution) can hide under the main signal.

It is also important: the HPLC purity says how much of the main component is present, but not what this main component is. It measures quantity, not identity.

HPLC purity = area percent (target signal divided by total signal).
Only an estimate: co-eluting impurities can remain hidden.
Says how much of the main substance is present - not what it is.

Purity is not identity

The most consequential error of thinking is: "99 % pure means 99 % the right peptide". That is not true. A sample can consist 99 % of a uniform substance - and still be the wrong peptide. HPLC purity alone cannot reveal this.

Identity requires other methods: above all mass spectrometry (MS or LC-MS), which measures the actual molecular weight and compares it with the theoretical value, supplemented by amino acid analysis or sequencing. Robust quality control therefore always combines both: HPLC for purity and MS for identity. If a CoA shows only an HPLC purity without any proof of identity, half the information is missing.

"99 % pure" can mean 99 % of the WRONG peptide.
Identity requires mass spectrometry (MS/LC-MS), amino acid analysis, or sequencing.
Good quality control = HPLC (purity) PLUS MS (identity).
Purity without proof of identity is only half the truth.

Net peptide content, sterility, and endotoxins

Besides purity, there is a second, often confused figure: the net peptide content. It indicates what proportion of the powder is actually peptide. Counterions (for example from trifluoroacetic acid or acetate), bound water, and salts make up a noticeable part of the powder mass and do not count toward the peptide. A sample can therefore be chromatographically highly pure and still have a lower net peptide content - these are two different figures.

With liquid or injectable preparations, further tests that are decisive for safety are added: sterility, the test for bacterial endotoxins (LAL test per pharmacopoeia), and the appearance. If these entries are missing from a product advertised as injectable, that is a serious warning sign. The note "for research purposes only / not for human use" also means that the product has undergone no regulatory quality and safety testing whatsoever.

Net peptide content is not the same as purity: salts, counterions, and water count toward the powder mass.
Injectables additionally require: sterility, endotoxin test (LAL), appearance.
Missing sterility/endotoxin data on "injectable" products is a warning sign.
"Research use only" = no regulatory testing, not validated for humans.

Red flags - and why gray-market certificates are often worthless

Many CoAs circulating on the internet do not stand up to critical scrutiny. Typical red flags: no independent third-party laboratory (the supplier tests itself), missing, reused, or copied batch numbers, no method specifications, inconsistent data, pure image files without verifiable provenance, and a purity figure without any proof of identity (MS) or sterility.

That this mistrust is justified is shown by independent analyses. In a study of over-the-counter, online-sold semaglutide published in 2024 in the Journal of Medical Internet Research, the actual purity, despite a "≥ 99 %" claim, was only around 8 to 14 %, the active-ingredient content well above the declaration, and endotoxins were detectable in all samples. Authorities such as the FDA also repeatedly warn against unapproved, "compounded" variants with unknown impurities and inconsistent salt forms. In short: a pretty PDF does not replace tested quality - and a CoA from the same hand that sells the product is at best a start, not proof.

Red flags: no third-party lab, missing/copied batch numbers, no method, only an image, purity without identity.
JMIR analysis 2024: over-the-counter online semaglutide only ~8-14 % pure despite "≥99 %", endotoxins in all samples.
Authorities (FDA) warn against compounded variants with unknown impurities.
A CoA from the seller itself is a start, not proof.

Related substance profiles

BPC-157

Synthetic peptide — predominantly animal data, NOT approved for humans.

TB-500 / Thymosin β4

Actin-binding peptide — research substance, NOT approved.

Semaglutid

GLP-1 receptor agonist — approved, prescription-only.

Frequently asked questions

Does "99 % purity" on the CoA mean the product is safe and genuine?: No. First, HPLC purity is only an estimate (area percent), under which impurities can hide. Second, purity says nothing about identity: 99 % pure can mean 99 % of the wrong peptide. Without mass spectrometry and - for injectables - sterility and endotoxin testing, "99 %" is worth little.
What is the difference between purity and net peptide content?: Purity (by HPLC) describes what proportion of the detected substance is the target substance. The net peptide content describes what proportion of the total powder mass is actually peptide - the rest is salts, counterions, and water. These are two different figures that a good CoA reports separately.
Can you trust a CoA from the seller?: Only with caution. A certificate produced by the supplier itself or circulated as a mere image file, without an independent third-party laboratory, without a batch number, and without proof of identity or sterility, is not a reliable piece of evidence. Independent analyses have repeatedly found large deviations from the certificate figures in gray-market goods.

Sources

This article is for information and education only. It does not replace medical advice and deliberately contains no dosing, usage or sourcing information.

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