Reading a CoA: interpret an HPLC lab test

✦ In short

What is a CoA and how do you read an HPLC lab test? Purity, mass spectrometry and independent lab verification explained step by step. RUO.

Research context (RUO): This guide explains how to read a certificate of analysis (CoA) and an HPLC lab test. All peptides at Peplife are supplied exclusively for in-vitro laboratory research and are not intended for human or animal use.

What is a CoA and how do you read a peptide's HPLC lab test?

Simplified step-by-step plan for reading a COA and HPLC lab test.

Reading a CoA lab test sounds more technical than it is: once you know where the purity, the identity and the source of the test are, you can recognise within thirty seconds whether a certificate of analysis is reliable or not. A certificate of analysis (CoA) is the document that shows what is really in a vial. For researchers working with peptides, this is the most important quality control that exists, because the purity and identity of the material determine whether experimental results can be trusted at all. In this guide we go step by step through the key components: HPLC purity, mass spectrometry, what constitutes a good value, and how to verify a CoA.

What is a CoA (certificate of analysis)?

A CoA is a formal laboratory document that confirms the identity and quality of a product with documented measurement results. It gives the recipient the assurance that the analysed material really is what the label claims. A CoA for a peptide typically states: the name and lot number (batch) of the substance, the test date, the performing laboratory, the measurement methods used and their outcomes. The two core measurements are almost always a HPLC analysis for purity and a mass-spectrometry analysis for the identity. A CoA without a lot number, without a lab name or without these two graphs says little in practice.

HPLC: how purity is measured

HPLC stands for high-performance liquid chromatography, or high-performance liquid chromatography. The technique separates the components of a mixture by sending the sample under high pressure through a column of adsorbent material. Each component reacts slightly differently with that material and therefore emerges at the other end at a different moment — that moment is called the retention time. A detector records each component as a peak in a graph, the chromatogram, and the area under each peak is proportional to the amount of that substance.

For purity this means: the laboratory counts the area of the main peak (the desired peptide) and compares it with the total area of all peaks together. If the main peak is 99% of the total, the reported purity is 99%. The remaining 1% are impurities, degradation products or synthesis residues that become visible as smaller peaks. A good chromatogram therefore shows one clear, sharp main peak with as few small side peaks as possible next to it.

Mass spectrometry: are the identity and molecular mass correct?

HPLC tells how pure a sample is, but not automatically what exactly the main peak is. That is what mass spectrometry (MS) is for. This technique measures the mass-to-charge ratio of ionised molecules and thereby calculates their exact molecular mass. Every peptide has a known, calculated molecular mass based on its amino acid sequence. If the measured mass on the spectrum matches that theoretical value, it is confirmed that the main peak really is the intended peptide and not another substance that happens to have the same retention time.

On a CoA, in the MS section you usually see two numbers side by side: the theoretical mass (calculated) and the found mass (measured). If they are close to each other, the identity is correct. In this way purity (HPLC) and identity (MS) check each other: together they show that the right peptide is present and how pure it is.

What is a good purity?

For research peptides, in practice an HPLC purity of 98% or higher is considered good, and many quality suppliers aim for 99%+. A lower value is not by definition worthless, but the higher the impurity percentage, the greater the chance that by-products influence experimental measurements. Important to know: 100.0% barely exists in practice. A CoA that claims exactly 100%, or shows a suspicious, perfectly smooth peak without any noise, actually deserves an extra critical look. Realistic certificates show small side peaks and a real figure such as 99.1% or 98.7%.

Why independent testing matters

A CoA is only as reliable as the party that performed the test. When a supplier tests its own product and draws up the certificate itself, there is a clear conflict of interest — it is a case of marking one's own homework. That is why a test from a independent, specialised laboratory more heavily. ISO/IEC 17025 — requirements for testing and calibration laboratories is the international standard against which such laboratories are assessed; an accredited lab performs HPLC and MS analyses under a demonstrable quality system. A CoA from such an independent external laboratory means that an impartial third party has established purity and identity, independently of the seller. How to find and check an independent lab report online yourself is explained step by step in how to recognise an independent CoA.

At Peplife every relevant batch is independently HPLC-tested and the accompanying CoA is verifiable per batch. That we take transparency seriously is also clear from how we deal with poor results: read, for example, why we rejected an entire batch when a lab analysis did not meet the standard. A supplier that only shows nice certificates but never a rejection tells only half the story.

How to verify a CoA (QR code and public verification)

A PDF of a CoA is easy to edit or falsify. That is why serious labs offer a public verification: a lot number or code with which the original report can be requested directly from the testing lab, often via a QR code or an online input field on the laboratory's own site. The practical check consists of a few steps. First check whether the lot number on the vial matches the one on the certificate. Then find the source: is the report directly with the independent lab and not just as a loose PDF on the webshop? Finally, scan the QR code or enter the code on the laboratory website and see whether the purity and identity match one-to-one with what the seller shows. If the figures differ, the lot number is missing, or the QR code leads nowhere, caution is warranted.

Do you want to understand exactly what you are testing before comparing certificates? Then first read what peptides exactly are, so that the concepts of amino acid sequence and molecular mass fall into context.

Frequently asked questions about reading a CoA lab test

What does HPLC purity mean on a CoA?
It is the percentage of the total peak area in the chromatogram taken up by the desired peptide. 99% purity means that 99% of the measured material is the intended peptide and 1% consists of impurities.

Why are there two measurements (HPLC and MS) on a CoA?
HPLC measures how pure the sample is, mass spectrometry confirms the identity by comparing the measured molecular mass with the theoretical value. Together they show both the quantity and the nature of the substance.

Is 100% purity realistic?
Rarely. Analytical methods almost always show tiny side peaks. A realistic figure such as 98.9% or 99.2% is more credible than an exact 100% claim without any noise in the chromatogram.

Why does an independent external lab matter?
Because a seller who tests their own product has a conflict of interest. An independent laboratory establishes purity and identity impartially, which greatly increases the reliability of the certificate.

How do I check whether a CoA is genuine?
Compare the lot number on the vial with the one on the certificate and use the test lab's public verification or QR code to open the original report directly at the source. Matching numbers and a working verification link are good signs.

What if the lot number on the vial and the CoA don't match?
Then the certificate may belong to a different batch and says nothing about the material you have in hand. A matching lot number is the basis of every reliable verification.

What is a CoA? How to read a peptide's HPLC lab test