What is the difference between purity and content on a peptide certificate?

Purity is a percentage: the target peak's share of the total integrated HPLC peak area. Content is a quantity in milligrams: how much peptide the lab actually measured in the vial. Purity tells you how clean it is; content tells you how much there is. A vial can be highly pure and still hold less than the label says, so the two answer different questions.

Can a peptide be 99% pure and still underfilled?

Yes. Purity is a ratio calculated from whatever material is in the vial, so a vial filled with 8 mg of peptide instead of 10 can still show a 99% pure chromatogram. The purity figure is real and the fill is short at the same time, because a percentage cannot measure quantity. Only a content test compares the amount against the label.

What is net peptide content?

A dried synthetic peptide is usually a salt: it carries a counterion, most often trifluoroacetate from the TFA used in purification, plus some residual water. Net peptide content is the mass of the peptide alone, after subtracting counterion and water. Gross weight is everything in the vial. The net figure is the most conservative reading of how much peptide you actually have.

Does a high purity number guarantee I am getting the labelled amount?

No. Purity and quantity are independent. A high purity figure says the material present is clean, not that there is as much of it as the label claims. The only number that speaks to the labelled amount is the measured content, so a purity-only certificate leaves the quantity question open.

Do you publish the measured content for your products?

Yes. On our lab reports page, 57 of the 58 published reports print the measured milligram value on the certificate, next to the purity figure, so you can compare it to the label yourself. We do not round the measured content to the label or remove it when it is not flattering.

Are your vials overfilled or underfilled?

Among the comparable single-peptide results we publish, most measure at or above their label, some come in under, and the reported shortfalls are single-digit percentages, with the exact figure shown on the certificate rather than hidden. The reason we can answer this is that the reports we publish include measured content, not only purity.

Is content the same as potency or activity?

No. Content is a mass measurement: how many milligrams of peptide are present. Potency or biological activity is a functional question that a mass measurement does not address, and it is not something a research-use certificate of analysis reports. Content answers how much, not how active.

Why can a purity figure on its own be misleading?

Because purity is a proportion, not a quantity. A vial can show a high purity and still be short of its labelled milligrams, and the purity number has no way to reveal that. Only a measured content figure checks the labelled amount, so a purity figure alone can look reassuring while leaving the quantity untested. Comparing the two, where both are present, is what tells you the fuller story.

Does a blend report content differently?

Yes. A blend certificate reports the measured content of each peptide component separately, so a single blend can list several milligram figures. That is why you cannot compare a blend's total label weight to one component's measured value; each component has its own content line on the report.

What should a good certificate include on this question?

Ideally a purity percentage and a measured content in milligrams, and where possible a distinction between gross weight and net peptide content. Together these let you judge both how clean the material is and how much of it there is. A certificate with purity alone has answered only half of it.

Where can I see purity and content together for your batches?

On our lab reports page, where each batch lists its purity figure and, for almost all of them, the measured content in milligrams, with the testing lab named and a verification link where the lab provides one. The comparison to the label is yours to make from the published numbers.

Purity Is Not Content: What Is Actually in the Vial

Q: Why does the counterion matter for how much peptide I get?

Because the counterion and residual water are part of the powder's weight but not part of the peptide. A vial can weigh out to its label in gross powder while the actual peptide mass is lower. That is why a careful certificate is clear about what its content figure measures, and why net peptide content is worth knowing about.

Q: Why do some certificates show only purity and no milligram figure?

Because a content assay is a separate, more involved measurement than a purity run. A certificate can state a high purity and never test the quantity, which leaves the label's milligram claim unverified. On our own page, 57 of 58 reports include a measured content value for exactly this reason.

Q: How can I tell if a vial is underfilled?

Look on the certificate for a measured content or assay figure in milligrams and compare it to the label. A vial labelled 10 mg is at or above label when the measured content is 10.0 mg or higher; a result below 10.0 mg is under label, however pure it is. If the certificate reports only a purity percentage, the fill cannot be checked from it at all.

Open a peptide certificate and the number that stands out is purity: "99% pure". It is a real measurement, and it is also the answer to only one of the two questions that matter. The other one, how much peptide is actually in the vial, is a different number entirely, and a vial can score well on the first while falling short on the second.

Purity is a percentage. Content is a quantity. A certificate can carry one without the other, and the gap between them is where "99% pure" stops telling you what you paid for.

TL;DR: purity, content and net peptide content are different

Purity is a ratio. It is the target peak's share of the total integrated HPLC peak area, not how much peptide there is. Content is a measured mass in mg. It is the milligram figure the lab measured for the vial, which is what a label like "10 mg" is claiming, and a different question from purity. A vial can be pure and underfilled. 99% purity says nothing about whether the vial holds 10 mg or 8 mg. Net peptide content is a third number. Gross weight includes peptide, counterion and residual water; net peptide content is the peptide alone. We publish measured content on 57 of our 58 reports. Each figure sits next to the purity figure on our lab reports page, so you can compare it to the label yourself.

Two questions, two numbers

Picture two vials, both labelled 10 mg.

The first is 99.5% pure but the lab measured 8.7 mg of peptide in it. It is a clean peptide, and there is less of it than the label says.

The second is 97% pure and the lab measured 10.2 mg. It is slightly less pure, and there is slightly more peptide than the label promised.

Purity alone ranks the first vial higher. Content flips the comparison. Neither number is wrong, they simply answer different questions: purity asks "of what is here, how much is the target?", content asks "how much target is here at all?" You need both to know what is in the vial, which is why a certificate that reports only purity has answered half the question. We go through where each of these sits on a real document in reading a certificate field by field.

How purity can look perfect while content falls short

Purity is a chromatographic ratio: the target peak's share of the total integrated peak area, which we cover in how to read an HPLC chromatogram. It is calculated from the material that is actually there. If a vial was filled with 8 mg of peptide instead of 10, the chromatogram of that 8 mg can still be 99% one clean peak. The purity is real. The fill is short. The percentage has no way to tell you that, because it is a proportion of whatever was loaded, not a measurement against the label.

That is the whole reason content is a separate test. It weighs the peptide against a reference to answer the quantity question directly, and it is the only number on a certificate that speaks to whether "10 mg" on the label is true.

Why purity and quantity are separate tests

A content assay is a separate, more involved measurement than a purity run. So a certificate can state a high purity and never test the quantity, which leaves the label's milligram claim unverified. On our own lab reports page, 57 of 58 published reports carry a measured content value, precisely because the quantity question is the one a purity number cannot answer.

Net peptide content: the third number

Even a measured milligram figure can mean two different things, and the distinction is worth knowing.

A dried synthetic peptide is usually a salt. During purification it picks up a counterion, most often trifluoroacetate from the TFA used in the mobile phase, and it holds some residual water. So the powder in the vial is peptide plus counterion plus water. The gross weight is everything in the vial. The net peptide content is just the peptide part, after subtracting counterion and water.

The gap is not trivial: counterion and moisture can account for a meaningful share of a lyophilised peptide's weight. A vial can weigh out to its label in gross powder while the actual peptide mass is lower. This is why a careful certificate distinguishes the measured content it reports, and why "net peptide content" is the most conservative reading of how much peptide you actually have. It connects to the counterion point we make in our HPLC-versus-mass-spec explainer.

What our own reports show, and why we publish the number

We do not hide the content figure, and we do not round it to the label. On our lab reports page, 57 of the 58 published reports print the measured milligram value on the certificate, directly next to the purity figure.

Read across those reports and the picture is what you would hope for and honest about where it is not: among the comparable single-peptide label-versus-measured results on the page, most are at or above label, some are below, and the reported shortfalls are single-digit percentages, with the figure shown rather than buried. That is the point of publishing content at all. A vendor who tests only purity can call a short-filled vial "99% pure" and be telling the truth while leaving the quantity unstated. Publishing the measured milligrams, whatever they are, is what lets you check the label instead of trusting it.

None of these products are approved medicines, and none of this is a dosing or safety statement. It is about one thing: whether the quantity on the label is a claim or a measurement.

How to check it yourself

Find the content figure, not just the purity

On a certificate, look past the purity percentage for a milligram value, often labelled content, assay or quantity. If there is only a percentage, the label's quantity claim has not been tested.

Compare it to the label

A vial labelled 10 mg is at or above label when the measured content is 10.0 mg or higher; a result of 8.7 mg is under label, however pure it is. The comparison only works if the content number is there to compare.

Note whether it is gross or net

If the certificate distinguishes net peptide content from gross weight, the net figure is the conservative one. If it does not state the basis, do not assume the measured content is either gross or net.

Products and Categories Referenced

Every batch below has its purity and its measured content published together on our lab reports page.

Longevity & Anti-Aginglongevity

Mitochondrial function, NAD+ metabolism, telomere maintenance

SS-31longevity

Mitochondria-targeted tetrapeptide (Elamipretide) that stabilizes cardiolipin and prevents ROS formation at the source.

GHK-Culongevity

Naturally occurring copper tripeptide complex for skin regeneration and anti-aging research. Stimulates collagen synthesis, accelerates wound healing, and modulates 4000+ genes. Plasma levels decline with age, making it a key target in longevity research.

NAD+longevity

Essential cellular coenzyme that declines with age. Powers energy metabolism in every cell, activates sirtuins (longevity genes), and supports DNA repair. A cornerstone molecule in aging and longevity research.

GLOWregeneration

3-in-1 skin peptide blend: GHK-Cu 50mg + BPC-157 10mg + TB-500 10mg. Targets collagen synthesis, tissue regeneration, and skin repair for comprehensive dermatological research.

Tirzepatidemetabolic

A first-in-class dual GIP and GLP-1 receptor agonist, and one of the most extensively studied compounds in modern metabolic and weight-regulation research. Supplied as a lyophilised research peptide with a per-batch certificate of analysis, for laboratory and in-vitro use only.

Batches with purity and content published together