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A COA should answer more than one question.

Most research-peptide sites reduce “quality” to a single purity number. But purity alone cannot establish identity, net content, sterility or batch consistency. This page explains what a complete analytical characterization actually involves — so you can read any Certificate of Analysis critically, including ours.

Identity ≠ Purity ≠ Net Content

These are three separate analytical questions. Conflating them is the most common way a COA can look impressive while leaving the important questions unanswered.

Identity
Is the material actually the claimed compound?
Typically: LC–MS / mass confirmation
Purity
What % of the detected peptide-related material is the main compound?
Typically: RP–HPLC (% main peak)
Net Content
How many milligrams of the target compound are actually present?
Typically: quantitative assay
Why it matters: A vial can be 99% pure and still contain more or less than its label claim — because purity is a ratio, not an amount. A report that shows 99% purity but no net-content assay has not told you how much compound you actually have.

What a complete characterization can include

IdentityLC–MS / MS²

Confirms the molecule is what the label says by measuring its mass. Retention-time comparison and mass confirmation distinguish the target peptide from unrelated material or the wrong sequence.

PurityRP–HPLC / UPLC

Measures the percentage of detected peptide-related material that corresponds to the principal compound. Impurities such as truncated or deletion sequences appear as additional peaks.

≥99% HPLC purity is the specification documented on every VP Peptides batch.

Net Content / AssayQuantitative

Answers how many milligrams of the target compound are present — distinct from purity. Example: a 30 mg label with a measured content of 31.3 mg tells you the actual amount, which a purity figure never can.

SterilityUSP <71>

Evaluates the presence or absence of viable microorganisms under defined test conditions; the compendial acceptance criterion is “No Growth.” A responsible report states the specific lot tested rather than a generic “sterile” claim.

Bacterial EndotoxinsUSP <85>

Detects and quantifies Gram-negative bacterial endotoxin. A numeric result — for example, a value in EU per milligram — is far more informative than a simple PASS.

VP Peptides batches document an endotoxin result (specification < 1 EU/mg).

Elemental ImpuritiesUSP <232>/<233> · ICP–MS

Screens for heavy metals such as lead, cadmium, mercury and arsenic, typically by ICP–MS against defined limits. “Heavy-metal free” is not a meaningful claim without the elements, method and limits shown.

VP Peptides batches document a heavy-metals result (specification < 50 ppb).

Water / Residual MoistureUSP <921> · Karl Fischer

Residual moisture in a lyophilized material affects its chemical and physical stability over time. Water determination characterizes how dry the material is — a stability signal that purity alone does not capture.

Content UniformityBatch-level

A single vial tested is not the same as a batch verified. Testing one unit characterizes that unit; batch consistency is a separate question that one-vial results cannot answer.

One-vial result ≠ batch uniformity. A COA characterizes the specific sample that was tested. That is valuable — and it is also a boundary worth stating plainly rather than implying every vial is identical.

Where the documentation comes from

Not all “lab tested” claims are equal. The source of a report changes how independently it can be verified.

Level 1
Supplier documentation
Testing supplied by the manufacturer or vendor of the material.
Level 2
Third-party documentation
An independent report from an external laboratory, supplied alongside the material.
Level 3
Independent verification
A sample independently submitted for testing, rather than relying only on documentation received.

VP Peptides publishes independent third-party analysis by Lingke Bio-Detection and ships a batch-level Certificate of Analysis with every order. See recent verified batches.

“Not Tested” is a result

Transparency means showing what was measured and what was not. A batch with identity, purity and content data but without a given test should say Not Tested for that field — not leave it blank or imply a pass. An honest gap is more trustworthy than a wall of green badges.

CharacteristicWhat it provesReference
IdentityCorrect moleculeLC–MS
Purity% main compoundHPLC
Net contentmg actually presentAssay
SterilityNo viable microorganisms (lot)USP <71>
EndotoxinsGram-negative endotoxin levelUSP <85>
Elemental impuritiesHeavy-metal limitsUSP <232>/<233>
WaterResidual moisture / stabilityUSP <921>

Read the full COA guide

Frequently asked questions

Does 99% purity mean the vial contains 99% of its labeled amount?

No. Purity and net content are different measurements. Purity is the percentage of detected peptide-related material that corresponds to the target compound; net content is how many milligrams of the target compound are actually present. A vial can be 99% pure and still contain more or less than its label claim.

What is the difference between identity, purity and net content?

Identity asks whether the material is actually the claimed compound (typically confirmed by mass spectrometry). Purity asks what fraction of the detected material is the main compound (typically by HPLC). Net content asks how many milligrams of that compound are present. All three are separate analytical questions.

What does a sterility or endotoxin result mean on a COA?

Sterility testing (for example under USP <71>) evaluates the presence or absence of viable microorganisms under defined conditions. The bacterial endotoxins test (USP <85>) detects and quantifies Gram-negative bacterial endotoxin, reported as a numeric value such as EU per milligram. A quantitative value is more informative than a simple PASS.

Why does “Not Tested” matter?

Transparency means showing what was measured and what was not. If a batch has identity, purity and content data but a given test was not performed, that should be stated as “Not Tested” rather than left blank or implied to pass. An honest gap is more trustworthy than a wall of green badges.

Research use only. This page is educational information about analytical characterization and quality documentation. VP Peptides products are furnished for laboratory research purposes only; they are not drugs, foods, or cosmetics, are not for human or veterinary use, diagnosis, treatment or administration, and nothing here is medical, dosing, or safety advice. References to USP General Chapters are educational; the specific tests documented for any material are those shown on that material’s Certificate of Analysis.