Reading a Certificate of Analysis
A Certificate of Analysis (COA) is the document that tells you exactly what's in the vial. It's not marketing copy — it's a record produced by the testing laboratory after analytical work has been completed on a specific batch.
If you've never read one before, this guide walks through every field on a typical peptide COA and what it means for your research.
Header section
Compound name and CAS number
The chemical name of the peptide and (where applicable) its CAS Registry Number — the unique chemical identifier. Confirm this matches the product you ordered before going further.
Batch (lot) number
The unique identifier for this specific manufacturing batch. Cross-reference the batch number on the COA with the lot number printed on the vial label. They must match. If they don't, contact us before using the product.
Manufacturing date and date of analysis
Manufacturing date is when the peptide was synthesized. Analytical date is when the testing laboratory ran the assay. The analytical date is always later than the manufacturing date.
Issuing laboratory
The name of the third-party laboratory that performed the analysis. This is not Rewerk — we use independent labs for verification. You can contact the lab directly for raw analytical data if you need it for your records.
Purity — HPLC
Method
High-performance liquid chromatography (HPLC) is the standard method for quantifying peptide purity. The COA will list:
- Column type — typically a C18 reversed-phase column for peptide separation.
- Mobile phase — usually a water/acetonitrile gradient with 0.1% TFA.
- Detector — UV at 214 nm or 220 nm (peptide bond absorption).
- Gradient profile — the time-vs-organic-percentage program.
Result
The purity result is expressed as a percentage — the area of the main peak divided by the total area of all peaks on the chromatogram. Rewerk products are released at ≥99% purity by HPLC.
The chromatogram itself may be included with the COA. If not, contact us with the lot number and we'll send the raw trace.
Identity — Mass Spectrometry
Method
Mass spectrometry confirms the molecular identity of the peptide by measuring its mass-to-charge ratio. The COA will list the instrument and ionization method (commonly ESI-TOF or MALDI-TOF).
Expected vs. observed mass
Two numbers are given:
- Expected mass: calculated theoretical mass of the target peptide.
- Observed mass: measured mass from the sample.
These should agree within the instrument's accuracy (typically < 0.1 Da for TOF instruments). A significant discrepancy means the peptide is not the intended structure.
Physical & chemical specifications
Most COAs also report:
- Appearance: typically "white to off-white lyophilized powder."
- Solubility: compatible solvents and dissolution behavior.
- Water content (Karl Fischer): residual moisture, typically < 6%.
- Counter-ion content: usually TFA or acetate, depending on synthesis route.
- Net peptide content: the proportion of the powder that is actually peptide (the rest is water, counter-ion, and salts). Important for accurate mg/mL dosing calculations.
Conclusion / release statement
The COA ends with a release statement from the issuing analyst confirming the batch meets specification. Look for the analyst's signature, initials, or credential and the date.
Red flags
A COA should not raise questions. If you see any of these, contact us before using the product:
- Lot number on COA does not match vial label.
- Purity result below the spec listed on the product page.
- Observed mass differs significantly from expected.
- Missing analytical method details, laboratory name, or analyst signature.
- COA dated before the manufacturing date.
Where to find your COA
Every Rewerk product page has the COA linked publicly. Browse the full COA library →
Research use only
COA values describe the chemical specification of the research material. They are not instructions for human or animal use, and Rewerk products are intended exclusively for in vitro laboratory investigation.