Reading Certificates of Analysis — what to look for, what to question

The Certificate of Analysis (COA) is the document that lets a researcher verify a research peptide supplier's claims before bench use. A trustworthy COA includes specific elements; a weak COA either omits those elements or hides them behind marketing language. This article walks through the COA fields field-by-field, identifies common omissions, and outlines the verification questions worth asking before placing a research order.

Field-by-field: what should be on every COA

Compound name and batch identifier

A trustworthy COA names the compound (including any salt form), the manufacturer or supplier, and a unique batch identifier. The batch identifier should be specific enough to resolve back to a single manufacturing lot — at Nexus, the format is NEX-COMPOUND-YEAR-SEQUENCE, e.g., NEX-BPC-157-2026-0405. This field is what lets a researcher distinguish "I have BPC-157" from "I have lot 0405 of BPC-157 manufactured in 2026."

Manufacturing date and expiry date

ISO 8601 dates with both manufacturing and projected expiry. The expiry date assumes specified storage conditions; lyophilized peptides at -20°C typically carry 2-4 year expiry windows. Without an expiry, the COA cannot be used to plan research timing.

Net peptide content per vial

Net peptide mass per vial, excluding counterion and excipients. This is the number that matters for stoichiometric research — a 10 mg vial of an acetate-salt peptide contains slightly less than 10 mg of acetate-salt material because the 10 mg is net peptide. The COA should clarify which interpretation is used.

HPLC area-percent purity

Numeric area-percent purity (e.g., 99.65%) accompanied by the method (column, mobile phase, gradient, detection wavelength) and retention time. Without the method, the percentage cannot be compared across suppliers or batches.

Mass spectrometry expected vs observed mass

Two numeric values — expected molecular mass calculated from sequence, observed mass measured experimentally — with the ppm or Da error and the ionization method (typically ESI for peptides). Without observed mass, identity has not been confirmed.

Endotoxin testing result

For research peptides destined for cell-culture or in-vivo-research applications, bacterial endotoxin content matters. The result is typically reported in EU/mg (endotoxin units per milligram) with the testing method (LAL gel-clot is standard for research peptides). A trustworthy COA either reports the value or states explicitly that endotoxin was not tested.

Testing laboratory identity and analyst signature

The independent laboratory that ran the analysis, the analyst who certified the results, and the date of certification. This is the field that distinguishes a third-party-tested compound from a self-certified one. A trustworthy COA names the lab; a weak COA either omits the lab or uses a laboratory that turns out to be the supplier's own internal QC unit.

Common omissions and what they signal

• Missing testing laboratory name. Most common omission. Suggests in-house QC was used, which carries a structural conflict of interest. Ask the supplier directly: which independent laboratory performed the analysis?
• Missing HPLC method details. Even when the area-percent value is published, the method (column, gradient, wavelength) often is not. Without it, the value cannot be cross-validated.
• Missing mass spectrometry expected vs observed comparison. Some COAs report only a "passed identity" qualitative statement without the numeric mass values. Without numeric mass, the identity claim cannot be verified.
• No batch identifier or generic batch identifier ("Batch 1"). Generic identifiers prevent batch-level traceability and resolution back to a specific manufacturing lot.
• No expiry date or vague expiry ("stable for several years"). Suggests the supplier has not characterized stability of the specific compound, only relied on generic peptide-class assumptions.
• Watermarked PDFs without parseable metadata. Some COAs ship as flat watermarked images of certificates, preventing programmatic verification. Trustworthy COAs are text-extractable.

Third-party verification standards

Beyond what is on the page, the question of who performed the analysis matters. A research-grade COA where the analysis was performed by the supplier's own QC department carries less verification weight than one performed by an independent contract analytical lab. The structural conflict of interest in self-certification is well-recognized in regulatory contexts (cGMP pharmaceutical manufacturing requires explicit independence rules) and applies even at research grade.

The Nexus verification model is third-party-first: every batch is tested by an independent contract analytical laboratory, the laboratory is named on the COA, and the analyst signature is the individual who certified the analysis at that laboratory. The verification model is documented in full on the Lab Verified page.

Verification questions worth asking

When evaluating a research peptide supplier, four questions about the COA process are worth asking before placing an order:

• Is the testing laboratory independent of the supplier? (Asks about structural conflict of interest.)
• Can I access the COA before purchase? (Asks whether documentation is gating — paywalled or login-walled documentation reduces verification weight.)
• Is the COA traceable to a specific batch I will receive? (Asks whether the documentation matches the lot, or whether it is a generic compound-level certificate.)
• What does the supplier do when a batch fails specification? (Asks about quality control rigor — release thresholds only matter if some lots are rejected.)

A trustworthy supplier answers all four affirmatively and concretely. A weak supplier either avoids the questions or answers vaguely. The Nexus answers: independent labs, public no-login COA archive, batch-specific COAs traceable through the verification URL, and a release threshold (typically ≥98% HPLC) that does reject lots when they miss it.