A certificate of analysis (COA) is the closest thing a research lab has to a passport for a peptide. It tells you what the material is supposed to be, how it was tested and what the results were. Yet many researchers in South Africa glance at the purity percentage, see a number above 98%, and move on. This guide walks through how to read a peptide COA properly: what HPLC purity really measures, why mass spectrometry matters just as much, and which red flags deserve a second look before material goes into your work.
Every product in our peptides South Africa collection is batch-tested by HPLC and mass spectrometry, so you can put the steps in this guide into practice with a real certificate.
What a peptide COA is (and what it is not)
A COA is a batch-specific test report. It should describe one production lot of one compound, tested by a defined method, with results recorded against that lot. It is not a marketing sheet, a generic product specification or a promise about how a compound will behave in an experiment. A COA tells you about identity and purity at the time of testing; storage, handling and transport after that point are your responsibility.
Biolabs publishes certificates for its compounds on the Biolabs COA page, including BPC-157, TB-500, GHK-Cu, Semax, MOTS-c, Tesamorelin, CJC-1295 + Ipamorelin and SS-31. It is worth opening the relevant certificate before you order, not after.
The fields every COA should show
- Compound name and sequence or structure. The name alone is not enough; a sequence or formula lets you check you are looking at the right molecule.
- Batch or lot number. This links the report to a specific production run.
- Test date. A very old report tells you less about material that is on the shelf today.
- Testing laboratory. Who ran the analysis, and ideally whether it was an independent lab.
- Methods used. Usually reversed-phase HPLC for purity and mass spectrometry (MS) for identity.
- Results with units. A purity percentage, an observed mass and the expected mass for comparison.
HPLC purity: what the percentage really means
High-performance liquid chromatography (HPLC) separates the components of a sample as it passes through a packed column. Different molecules leave the column at different times, and a detector, usually measuring UV absorbance, records each one as a peak on a graph called a chromatogram.
Reading the chromatogram
The horizontal axis is retention time, meaning how long each component took to come through the column. The vertical axis is detector response. In a clean sample you expect one tall, sharp main peak for the target peptide and, at most, a few very small peaks elsewhere on the baseline.
The purity figure is normally calculated by "area percent": the area under the main peak divided by the total area of all integrated peaks. So a result of 99.1% means that, under that method and detector setting, 99.1% of the detected signal came from the main peak.
What HPLC purity does not tell you
- It does not confirm identity on its own. A single clean peak shows the sample is mostly one thing, not that the one thing is the correct peptide.
- It is method-dependent. A different column, gradient or wavelength can separate impurities differently, so two labs can report slightly different numbers for the same lot.
- It is not the same as peptide content. Lyophilised peptides also contain water and counter-ions, which HPLC area percent does not count. A 99% pure peptide by HPLC is not 99% peptide by weight.
Mass spectrometry: confirming you have the right molecule
Mass spectrometry measures the mass-to-charge ratio of ionised molecules, which lets the lab compare the observed molecular mass with the mass expected from the peptide's sequence. This is the identity check that HPLC cannot give you.
As a worked example, BPC-157 has a molecular weight of about 1,419.5 g/mol. A COA for a BPC-157 vial should report an observed mass that lands very close to that expected value. Small differences of a fraction of a dalton are normal and depend on the instrument and whether average or monoisotopic mass is quoted. A difference of whole amino acids, or a recurring +16 Da shift, is a different story.
Common mass shifts and what they suggest
- Missing mass equal to one amino acid. A possible deletion sequence, where one residue failed to couple during synthesis.
- Extra mass equal to one amino acid. A possible insertion, often linked to excess reagents during synthesis.
- +16 Da. Commonly associated with oxidation, for example of methionine.
- Mass of a protecting group. Incomplete removal of a side-chain protecting group after synthesis.
These categories line up with the main classes of peptide-related impurities described in the review literature on solid-phase peptide synthesis, which lists deletions, insertions, diastereomers, protection adducts, oxidation products and dimers as the typical suspects.
Why impurities matter in research
It is tempting to treat a few percent of impurity as harmless background. In practice, the research record shows otherwise. One published investigation found that individual peptides bought from commercial custom suppliers for laboratory immunology assays were contaminated with a different peptide at roughly 1% by weight, enough to produce false-positive results in those assays. The authors recommended additional quality-control checks beyond standard chemical analysis.
The lesson for any lab is simple: purity and identity data are not paperwork. They are part of the experimental design, and they help explain unexpected results before you blame the model or the method.
Counter-ions, peptide content and the weight on the label
Most synthetic peptides are purified with reversed-phase HPLC using trifluoroacetic acid (TFA), so the final powder is often a TFA salt. Some suppliers exchange this for acetate. Either way, the counter-ion and residual water add weight. That is why "net peptide content", where it is reported, is usually lower than HPLC purity.
When you compare lots or suppliers, note whether the COA states the salt form and whether a peptide content figure is given. It matters most when you are preparing solutions to an exact concentration for an experiment.
Five red flags on a peptide COA
- No batch number, or a batch number that does not match what is printed on the vial or pen.
- No chromatogram, only a purity number with nothing to show how it was derived.
- No mass spectrometry result, so identity is never actually confirmed.
- A report that looks identical across different compounds, or an image that has clearly been edited.
- Purity of exactly 100%. Real analytical methods detect at least trace minor peaks.
Matching the COA to the format you buy
A COA describes the peptide material. Depending on the format, what you receive may also include a diluent or a device. For lyophilised material in our peptide vials collection, the COA relates directly to the powder in the vial. For ready-made formats such as the BPC-157 pre-filled pen in our pre-filled peptide pens collection, or a Semax nasal spray, the certificate still tells you about the peptide, while storage and the cold chain on arrival determine how well it stays that way.
For more on choosing between formats, read peptide pens vs vials in South Africa, and for the bigger supplier checklist see our research peptides South Africa buyer's guide.
Frequently asked questions
Is 98% HPLC purity good enough for research?
It depends on the work. Many labs treat 98% and above as a sound baseline, but the right threshold is set by your protocol. What matters as much as the number is a clean chromatogram and a mass result that confirms identity.
Why is net peptide content lower than HPLC purity?
HPLC area percent only compares the peptide with other detected components. Water and counter-ions such as TFA or acetate also make up part of the powder's weight, so the peptide content by weight is lower.
Can I trust a COA without mass spectrometry?
Treat it with caution. HPLC shows how pure a sample is, but only mass spectrometry, or an equivalent identity test, confirms that the main component is the correct peptide.
Where can I find Biolabs COAs?
Certificates for Biolabs compounds are listed by compound on the COA page.
Sources
- D'Hondt M, et al. Related impurities in peptide medicines. J Pharm Biomed Anal. 2014. PubMed 25044089
- Currier JR, et al. Peptide impurities in commercial synthetic peptides and their implications for vaccine trial assessment. Clin Vaccine Immunol. 2008. PubMed 18077621
Research use only: All Biolabs products are sold strictly for laboratory and research use only. They are not for human or veterinary use, not intended to diagnose, treat, cure or prevent any condition, and not for consumption. This article is for educational purposes and is not medical advice.