How to read a peptide certificate of analysis

A peptide certificate of analysis (COA) is the document that separates a supplier's claims from a laboratory's evidence. It records what was actually measured on one specific manufactured batch — the identity of the sequence, its chromatographic purity and, on more complete certificates, the composition of the lyophilised powder itself. For a laboratory sourcing research peptides in the UK, it is the most informative document a supplier can provide, and the first thing worth reading before any order is placed.

Reading one takes a few minutes once you know what each field means — and, just as importantly, what each field cannot tell you. This guide walks through a typical peptide COA line by line: the identity block, the RP-HPLC purity report, the supporting assays, and the red flags that should stop a purchase regardless of what the headline purity figure says.

A COA describes one batch, not a product line

Synthetic peptides are made in discrete production runs. Each run — each batch — has its own impurity profile, because small variations in synthesis and purification carry through to the finished material. Peptide batch testing therefore only means something at batch level: a certificate is a snapshot of one run, analysed at one point in time. It is not a property of the product line, and it does not transfer from one batch to the next.

This is why the batch number is the most important field on the entire document. A COA without a batch number describes nothing in particular, and a COA whose batch number does not match the vial in front of you describes something else entirely. A marketing page that quotes a purity figure for a product, rather than publishing the certificate for the batch being sold, is quoting a specification — a target — not a measurement.

The identity fields

The top of a certificate states what the batch is supposed to be. Expect to see the product name with any accepted synonyms, the amino acid sequence (usually in one-letter code), the CAS registry number where one has been assigned, and the molecular formula together with the theoretical molar mass calculated from it.

Identity is then confirmed by mass spectrometry (MS). The instrument measures the mass of the molecules in the batch, and the certificate reports this observed mass alongside the theoretical value. If the two agree within the tolerance of the instrument, the chains in the vial have the mass of the intended sequence.

A worked example makes this concrete. BPC-157 is a synthetic pentadecapeptide with the sequence GEPPPGKPADDAGLV, molecular formula C₆₂H₉₈N₁₆O₂₂ and a theoretical molar mass of about 1419.5 g/mol. A credible certificate for a BPC-157 batch states that formula and mass, then shows a measured mass consistent with them — reported either directly or as the ion the spectrometer actually detects, such as the singly protonated molecule. An observed mass that cannot be reconciled with the stated formula means the batch is not BPC-157, whatever the label says.

One convention to be aware of: instruments may report monoisotopic or average mass, which differ by roughly a dalton for a peptide of this size. A small discrepancy between two documents is often a difference in convention rather than a difference in material — but a careful certificate says which convention it is using.

The purity section: reading the HPLC purity report

Purity on a peptide COA is almost always determined by reversed-phase high-performance liquid chromatography (RP-HPLC). The analytical column separates the components of the batch, and a detector records a signal as each one elutes, producing a chromatogram — a trace of detector response against time. Every component appears as a peak, and the time at which a peak emerges is its retention time.

The purity figure is calculated by area: percentage purity is the area of the main peak expressed as a percentage of the total area of all peaks in the chromatogram. A batch reported at 99.2% by RP-HPLC means the main peak accounted for 99.2% of the summed peak area, with the remaining 0.8% spread across minor peaks — typically closely related synthesis by-products such as deletion or truncation sequences.

Two caveats follow directly from the method. First, the figure only covers what the detector can see under the stated conditions; components that do not absorb at the detection wavelength, or that co-elute with the main peak, are not counted. Second, purity says nothing about identity — a chromatogram with one clean peak proves the batch is homogeneous, not that it is the right molecule. That is why credible quality control pairs the chromatogram with mass spectrometry, a distinction unpacked in RP-HPLC vs mass spectrometry.

Other fields you may see

Fuller certificates go beyond identity and purity to describe the composition of the powder itself. None of these fields is a formality: together they account for the difference between the gross mass in a vial and the mass of peptide chains it actually contains — the subject of peptide purity vs net peptide content.

Red flags on a peptide COA

Some omissions are disqualifying on their own. When reviewing a certificate, treat any of the following as a reason to walk away:

• No batch number. The document cannot be tied to any physical material.
• One "representative" certificate reused across batches. This is a specification sheet dressed as a COA; it describes a batch you are not buying.
• Purity with no method stated. A bare "99%" is unverifiable. The certificate should say "by RP-HPLC" at minimum, and ideally state the column, gradient and detection wavelength.
• An observed mass that does not match the stated formula. Beyond the monoisotopic-versus-average convention, a mismatch means wrong identity, significant modification, or a careless document — all disqualifying.
• No issuing laboratory or analysis date. An unattributed, undated document cannot be checked with anyone, and there is no way to know how old the data is.

None of these flags proves a batch is bad. They prove the documentation cannot show it is good — which, for procurement purposes, amounts to the same thing. A wider due-diligence checklist covering company records and dispatch practice is in how to choose a UK research peptide supplier.

How NorthScientific handles certificates

Use the checklist above on any supplier, including us. NorthScientific does not currently publish independent third-party analysis for the material it holds; each catalogue entry states the name, format and fill weight, and the sequence or identifiers where those are established. Ask any supplier for the batch-specific document before you order, and read it against the fields described here.

All material is supplied strictly for laboratory research use, under the terms of supply — and a certificate should be read in that spirit: as the analytical record of a sealed research reagent, nothing more.

Materials referenced: BPC-157 · TB-500 · GHK-Cu · full catalogue