How to Read a Certificate of Analysis for a Recombinant Protein

Updated 2026-09-28

Lot number, methods and reported results: what each part of a recombinant protein Certificate of Analysis tells a laboratory buyer.

What a Certificate of Analysis Covers

A Certificate of Analysis (CoA) is a lot-specific document recording how one batch of material was tested and what was observed. It should identify the product name, catalogue number, lot number, date of manufacture and date of analysis. Each reported parameter is paired with the method used to obtain it. A CoA describes the lot in hand, not the catalogue item in general, so a buyer should match the lot number on the document to the label on the vial. Without that match, the data has no standing. Where a specification is stated, a lot passes when the measured result is ≥ the criterion for that parameter.

Methods Matter More Than Results

Two CoAs may report the same parameter through different techniques, and the figures are meaningful only alongside the method. Purity measured by SDS-PAGE and purity measured by HPLC answer different questions and are not interchangeable. The same applies to identity, which may be confirmed by mass spectrometry, peptide mapping or western blot. Read the method column before the result column. If a method is not stated, ask the supplier how the value was obtained and under what conditions, so the figure can be interpreted correctly rather than assumed.

What the CoA Does Not Tell You

A CoA is a record of testing, not a regulatory certificate. It does not by itself establish that a material is suitable for a particular application, nor does it replace an in-house qualification. It also says nothing about how the material will behave after reconstitution, freeze—thaw cycling or extended storage under your own conditions. Treat the CoA as the starting point of your incoming-goods check: confirm identity, review the lot data against your specification, and run the assay that matters for your workflow. Where a value is absent, ask.

Where certificates go wrong in practice

Most CoA problems are not falsifications; they are omissions and mismatches that accumulate into unusable documentation. The lot number on the certificate does not match the vial label, which usually means the wrong certificate was sent but occasionally means the wrong material was. The method column is missing, so a purity figure cannot be interpreted or compared. A specification column is present but no acceptance criterion, leaving the reader unable to tell whether the result passed. An endotoxin figure is quoted per millilitre while the protein concentration is quoted elsewhere, or not at all, so the two cannot be combined into the per-microgram figure a cell-based application needs. None of these prevent a purchase. All of them prevent you from doing anything useful with the document afterwards, which is the entire reason it exists.

A one-page incoming-goods record you will actually keep

The most useful document after the CoA is one you write yourself when the material arrives. Record the receipt date, the catalogue number, the lot number transcribed from the vial rather than from the paperwork, the quantity, and the storage location. Note the method used for each specification you intend to rely on, and mark which parameters you verified in house and how. Add a line for the reference or qualification status of the lot — whether it is the qualified lot, a newly arrived lot awaiting comparison, or a lot under investigation. Keep it alongside the analysis record rather than in a purchasing folder, because the people who need it are the people reading experimental data, not the people paying invoices. At the level of effort involved, this is the highest-return piece of documentation in a small laboratory.

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