How to read a peptide certificate of analysis
A glossary of the fields that appear on a certificate of analysis, each tied to a published standard or regulator page, followed by a checklist of questions to ask about any report.
ICH Q6A, Q2(R2) and Q3D are written for pharmaceutical drug substances and products; they are cited as published standards for what each COA field means, not as a statement that any given research peptide must follow them.
| Field | What it means | What to check | Source and retrieved date |
|---|---|---|---|
| Identity | The test that shows the material is the named compound and not a close relative. | Which method is named (for example mass spectrometry or a reference comparison) and whether identity rests on more than one retention time. | Source: ICH Q6A Retrieved October 7, 2026 |
| Identity by retention time alone | A single chromatographic retention time as the only identity evidence. | Whether identity relies only on one HPLC retention time, which ICH Q6A does not regard as specific. | Source: ICH Q6A Retrieved October 7, 2026 |
| Assay (content) | The measured content of the named substance. | That a content value is reported with the method used, separate from the purity percentage. | Source: ICH Q6A Retrieved October 7, 2026 |
| Purity and impurities (HPLC) | Chromatographic quantitation of the main component and its impurities. | That the report states the method, the detection setting and what the percentage is calculated from. | Source: ICH Q6A Retrieved October 7, 2026 |
| Endotoxin | A bacterial endotoxin test result for material meant to be injected or used in sterile settings. | Whether an endotoxin result is reported with the method named, or the line is blank. | Source: ICH Q6A Retrieved October 7, 2026 |
| Microbial limits | Counts of aerobic organisms, yeasts and molds, and absence of named objectionable organisms. | Whether microbial results appear and which acceptance criterion applies. | Source: ICH Q6A Retrieved October 7, 2026 |
| Water content | The measured water in the material. | Whether a water or moisture value is reported where the material is hygroscopic. | Source: ICH Q6A Retrieved October 7, 2026 |
| Residual solvents and impurities | Organic and inorganic impurities and leftover solvents from manufacture. | Whether a residual solvent result is reported and against which limit. | Source: ICH Q6A Retrieved October 7, 2026 |
| Elemental impurities | Trace metals assessed under a risk based control strategy. | Whether any elemental impurity result is shown and what it is compared to. | Source: ICH Q3D(R2) Retrieved October 7, 2026 |
| Method specificity | Whether the analytical method measures the intended analyte without interference. | That the report names the method and that a validated method is cited. | Source: ICH Q2(R2) Retrieved October 7, 2026 |
| Sample description, source and lot number | Which sample was tested and where it came from. | That the lot number on the report matches the vial label, with source and dates stated. | Source: FDA, 21 CFR 211.194(a)(1) Retrieved October 7, 2026 |
| Method statement | The testing method written down for each result. | That each result lists the method used. | Source: FDA, 21 CFR 211.194(a)(2) Retrieved October 7, 2026 |
| Identity and strength before release | Testing of identity and strength against final specifications before a batch is released. | That a specification is stated and each result is compared to it. | Source: FDA, 21 CFR 211.165(a) Retrieved October 7, 2026 |
| Expiration date | A date set from stability testing and tied to the stated storage conditions. | Whether an expiry or retest date is shown with storage conditions. | Source: FDA, 21 CFR 211.137(b) Retrieved October 7, 2026 |
| Pyrogen and endotoxin testing guidance | FDA guidance on testing components and finished products for pyrogens and endotoxins. | Whether a stated endotoxin result is paired with a named method. | Source: FDA guidance Retrieved October 7, 2026 |
Checklist for any certificate of analysis
- Does the report name the lab, the sample, the lot number and the dates?
- Does the lot number on the report match the vial label?
- Is identity shown by a method that can tell the compound from close relatives?
- Is the purity method named, with what the percentage is calculated from?
- Is a content (assay) value reported separately from purity?
- Is an endotoxin result reported with its method, or marked not tested?
- Are microbial, water, residual solvent and elemental impurity lines present, or marked not tested?
- Is each result listed with its method and its acceptance limit?
- Is an expiry or retest date shown with storage conditions?
- Can the report be checked with the lab that issued it?