Research use only. StarBio products are supplied strictly for in-vitro laboratory research by qualified professionals. They are not for human or veterinary use, not for diagnostic or therapeutic use, and have not been evaluated by the FDA. This article covers documentation and laboratory handling only — it is not usage guidance.

A Certificate of Analysis is the laboratory report for one specific batch of material. It is the difference between a supplier telling you a compound is 99% pure and a supplier showing you the measurement. If you work with research peptides, being able to read a COA quickly is one of the more useful skills you can have — it tells you what you actually received, not what a website banner claims.

1. Every certificate describes one batch

A COA is not a statement about a product line. It is the result for one specific batch of material, produced in a single run and tested as one population. Two batches of the same compound are two different populations, and each gets its own certificate.

So the first question is not what the purity figure says — it is whether the certificate in front of you describes the material in front of you. Suppliers handle that link differently. Some print a batch identifier on the vial label; others hold it in their release records and issue the matching certificate on request, keyed to your order. Either approach works, provided the supplier can tell you which batch filled your order and give you that batch document. A certificate that cannot be tied back to your material tells you very little, however good the number on it looks.

2. Identity: confirmed by mass

Identity answers a simple question — is this the compound named on the label? For peptides, identity is normally confirmed by mass spectrometry (MS). The report lists a theoretical (expected) molecular weight calculated from the amino acid sequence, and an observed molecular weight measured from the sample.

Those two figures should agree closely. Small differences are expected depending on whether the instrument reports an average or monoisotopic mass, and on which charge state or adduct is observed. A large discrepancy is a genuine red flag: it can indicate a different sequence, an incomplete synthesis, or a counter-ion difference the supplier has not disclosed.

3. Purity: measured by HPLC

Purity is normally reported from high-performance liquid chromatography (HPLC), most often reverse-phase HPLC with UV detection around 214–220 nm, where the peptide bond absorbs.

The number you see — for example 99.1% — is a relative area percentage. The instrument integrates the area of every peak in the chromatogram and reports the main peak as a share of the total. This is important to understand: it means purity is measured relative to everything else the detector can see under those conditions.

What HPLC area percent does not tell you: absolute peptide content by weight. Lyophilized material also contains residual water, counter-ions such as acetate or trifluoroacetate (TFA), and sometimes salts. A vial can be 99% pure by HPLC and still be meaningfully less than 99% peptide by mass. If your work depends on precise mass, look for a separate peptide content or amino acid analysis figure rather than inferring it from the purity percentage.

4. Read the chromatogram, not just the number

Where the actual trace is included, it is worth a look. A clean profile shows one dominant, symmetrical peak with a flat baseline. Things worth noticing:

• Shoulders on the main peak — often closely related impurities such as deletion or oxidation products that did not fully separate.
• A cluster of small late-eluting peaks — more hydrophobic impurities.
• A noisy or drifting baseline — can inflate or deflate integration, making the headline percentage less meaningful.
• Missing axis labels or run conditions — without the gradient, column, and detection wavelength, the result cannot be reproduced or compared.

5. Appearance and physical description

Most certificates record the physical form observed at release — typically a white to off-white lyophilized powder or cake. This is a simple check you can repeat yourself. Discoloration, obvious moisture, or a collapsed cake in material that should be a dry solid is worth raising with the supplier before use.

6. Dates and who ran the test

Check the analysis date and the name of the testing laboratory. Third-party analysis — testing performed by an accredited lab independent of the seller — carries more weight than an in-house sheet, because the party producing the number has no commercial interest in the result. An undated certificate, or one with no laboratory identified, is not verifiable.

A quick checklist

• Certificate is traceable to the batch your material came from
• Compound name and sequence match what you ordered
• Observed mass agrees with theoretical mass
• Purity method stated (HPLC) with a percentage and, ideally, the chromatogram
• Appearance recorded
• Analysis date present and recent relative to the batch
• Testing laboratory identified

StarBio keeps batch documentation on file for every compound we supply. Certificates are not included in the package and our labels do not carry a lot number — instead, send your order number through the COA request form and we will send the certificate for the batch your order was filled from. You can also browse the COA Library.