Anyone sourcing research peptides for laboratory use quickly runs into three recurring abbreviations: COA, HPLC and LC-MS. Understanding what each one actually documents — and what it does not — is central to evaluating whether a research compound is suitable for a given experimental protocol.
What a Certificate of Analysis Actually Certifies
A Certificate of Analysis (COA) is a batch-specific document produced after a sample of a manufactured lot has been tested. It typically records the identity of the compound, an assessment of purity, the analytical method used to reach that assessment, and the date and, where disclosed, the testing laboratory. A COA is a snapshot of one tested sample from one production lot — it is not a guarantee that every vial in that lot is chemically identical, and it says nothing about a compound’s behaviour once reconstituted, stored incorrectly, or used outside a controlled setting.
For a researcher, the practical value of a COA is comparability: it lets you record, alongside your experimental data, exactly what purity and identity profile the material had when it left quality control. This matters for reproducibility — if a colleague or a future you needs to repeat an experiment, the batch documentation is part of the material and methods record.
HPLC: Measuring Purity by Separation
High-performance liquid chromatography (HPLC) separates the components of a sample by passing it through a column under pressure, with different molecules travelling through the column at different rates depending on their chemical properties. The output is a chromatogram: a series of peaks, each corresponding to a distinct compound in the sample, with peak area used to estimate relative abundance.
In peptide quality control, HPLC purity is usually reported as a percentage — the target peptide’s peak area relative to the total peak area of everything detected. A HPLC purity figure describes how much of the detected material is the compound of interest relative to synthesis by-products, truncated sequences, or degradation products. It does not, on its own, confirm identity: two different molecules can, in principle, elute at similar retention times under a given method, which is why HPLC purity data is normally paired with an identity method.
LC-MS: Confirming Identity by Mass
Liquid chromatography–mass spectrometry (LC-MS) couples the separation step of HPLC with a mass spectrometer, which measures the mass-to-charge ratio of ionised molecules as they exit the column. This produces a mass spectrum for each separated component, and the observed mass can be compared against the expected molecular weight of the target peptide.
Where HPLC tells you how much of something is present relative to everything else detected, LC-MS tells you what that something actually is, based on its mass. Together, an HPLC purity result and an LC-MS identity confirmation form the basis of most peptide batch documentation, giving a research buyer both a quantitative purity estimate and qualitative confirmation that the detected peak corresponds to the expected molecule.
Reading Documentation Critically
When reviewing batch documentation, it is worth checking: whether the report is batch-specific (tied to a lot number) rather than a generic specification sheet; whether both a purity method and an identity method are represented; and whether storage and handling notes accompany the analytical data, since a compound’s measured purity at the point of testing does not describe how it will behave after transport or after reconstitution.
Documentation should be treated as one input into experimental design, recorded and archived alongside your other methodology notes, not as a substitute for your own laboratory’s quality checks where those are appropriate to your protocol.
Research Use Only. This article is provided for general scientific education. It does not describe or endorse any human or veterinary use, dosing, or clinical application.