Public COAs.
Batch by batch.

Why third-party Certificate of Analysis matters

The research-peptide market has a verification problem. Many suppliers publish purity claims (≥98%, ≥99%) but withhold the data behind those claims — no chromatogram, no mass spectrum, no signed report, no batch traceability. A purity number on a product page is not the same as a Certificate of Analysis. The Certificate is the document that lets a researcher verify the claim, and the laboratory that produced it should be independent of the seller.

In-house verification carries a structural conflict of interest: the same entity that benefits commercially from a high purity number is reporting it. Third-party verification breaks that conflict by routing the analysis through a lab with no commercial stake in the result. The Certificate then carries the testing lab's name, the analyst signature, the method, the date, and the raw value — all the data a researcher needs to verify the claim without trusting the supplier.

An honest Certificate of Analysis includes: the compound name and batch identifier, the manufacturing date and expiry, net weight, the HPLC method and area-percent result, the mass spectrometry method and the expected vs observed mass with ppm error, an endotoxin testing result with method, the testing laboratory's name, and a certified-by signature with date. Anything missing from that list is either a gap in documentation or an indication the test was not actually run. Nexus publishes the full set on every batch. The expected field-by-field structure is established in the USP general chapter on chromatography (USP <621>) and the broader Certificate-of-Analysis convention is documented on Wikipedia.

Reading a Nexus Certificate of Analysis

Every Nexus Certificate of Analysis follows the same field structure so researchers can compare batches across compounds. A walkthrough of the fields:

Batch ID (e.g. NEX-BPC-157-2026-0405)

Unique identifier in NEX-<compound>-<year>-<sequence> format. Resolves through the /verify/<batch> URL for third-party verification.

Manufacturing date / expiry date

ISO 8601 dates. Expiry assumes documented storage conditions; lyophilized peptides have multi-year stability at -20°C.

Net weight

Net peptide content per vial (e.g. 10mg). Excludes excipients and counterions.

HPLC purity (e.g. 99.65% area-percent)

Reverse-phase HPLC area-percent of the main compound peak relative to total UV-active peaks at the detection wavelength. Method, column, and retention time are published alongside the value.

Mass spectrometry (expected vs observed mass)

Deconvoluted ESI-MS molecular mass. Expected mass is calculated from the canonical sequence; observed mass is measured. Difference is typically reported in Daltons and ppm.

Endotoxin (LAL gel-clot)

Bacterial endotoxin screening result (e.g. <0.5 EU/mg) with method. Relevant for biologic peptides that may be used in cell culture research.

Testing laboratory + analyst signature

Independent third-party laboratory name, analyst, and certified-by date. This is the field that distinguishes a third-party COA from a self-certified one.

HPLC vs mass spectrometry — what each tells you

HPLC and mass spectrometry answer different research questions. HPLC measures how pure a sample is — the area-percent purity is the proportion of the main compound versus the sum of all UV-active peaks in the chromatogram. A 99% HPLC value means 99% of the detected material is the main peak; the remaining 1% may be related impurities, synthesis byproducts, or counterions.

Mass spectrometry answers a different question: is this the right compound? By comparing the observed molecular mass to the expected mass calculated from the published sequence or structure, MS confirms identity. A high HPLC purity number without MS identity confirmation is incomplete documentation — the compound could be 99% pure of the wrong substance.

Nexus publishes both on every Certificate of Analysis. HPLC demonstrates purity; MS demonstrates identity. Both are required for a research-grade compound, and both are measured by an independent third-party laboratory. For the underlying methodology, see the Wikipedia primers on high-performance liquid chromatography and electrospray ionization mass spectrometry.

Endotoxin testing — where it matters

Bacterial endotoxin is a contaminant that can be introduced during synthesis or handling — particularly for biologic research peptides. Endotoxin testing using the Limulus Amebocyte Lysate (LAL) gel-clot assay screens for the presence of lipopolysaccharide signal at quantifiable thresholds (typically <0.5 EU/mg for research peptides destined for cell culture or sensitive assays). The method is codified in the USP <85> Bacterial Endotoxins Test.

Not every research peptide application requires low endotoxin material — analytical chemistry workflows, mass spectrometry standards, and HPLC method development can tolerate higher endotoxin levels because the compound is not contacting living cells. Cell-culture research, receptor-binding studies in live preparations, and immune-system-related research models depend on low endotoxin material. Nexus tests every batch so a researcher can match the documentation to the planned application.

What we don't test for, and why

An honest verification scope statement requires being clear about what the Certificate of Analysis does not document:

• Sterility— research peptides ship as lyophilized powder, which is inherently low-moisture but not sterile-filled. Sterility testing is a separate methodology (USP <71> cultures) appropriate for sterile-filled solutions, not for lyophilized research material. Customers reconstituting for cell culture should use sterile-filtered solvent.
• Potency in living systems — the Certificate of Analysis documents the compound's analytical chemistry (purity + identity) but not its biological activity. Biological potency is a research question, not a manufacturing question — and the answer depends on the experimental system, not the supplier. Nexus does not test compounds in cells or animals.
• Therapeutic claims — Nexus does not test whether a compound treats, cures, prevents, or mitigates any condition. All Nexus compounds are supplied for in-vitro research only. The regulatory disclaimer at /legal/regulatory-disclaimer documents the compliance framing in full.
• Counterion content — synthetic peptides ship as acetate or trifluoroacetate salts (depending on manufacturing). The HPLC purity refers to the main peak, and the mass spectrometry confirms the peptide mass, but the counterion is not separately measured. For research applications where counterion matters (e.g. quantitative receptor-binding work), the supplier-stated salt form is the relevant data.

Documenting what the Certificate doesn't measure is, in our view, as important as documenting what it does. A complete picture of compound chemistry is the foundation for downstream research, and gaps in that picture should be visible rather than hidden.