01 /What a COA is
A certificate of analysis (COA) is a document issued by a third party laboratory that reports the test results for a specific batch of a substance. For research peptides, a COA usually covers identity, purity, water content, microbial limits, endotoxin level (sometimes), and counter ion content.
The COA is the only document that ties a number on a vial label to a verified composition. Without one, the label is a marketing claim. With one, the label is a chain of custody from manufacturer to analytical lab to you.
02 /Identity testing
Identity testing answers the question, is this molecule actually the molecule on the label? The standard methods are mass spectrometry (MS), high performance liquid chromatography (HPLC) with reference standard comparison, and sometimes nuclear magnetic resonance (NMR) for unusual modifications.
On a peptide COA, you want to see the observed mass within 1 Dalton of the theoretical mass for the named sequence. For a 5000 Dalton peptide, an observed mass of 5001 or 4999 is fine. An observed mass of 4985 is a problem. Check this number before purity, because identity failure means the rest of the document is irrelevant.
03 /Purity (the headline number)
Purity is the percentage of the sample that is the target peptide. The standard method is HPLC with UV detection at 214 nm (peptide backbone) and 280 nm (aromatic residues). The reported value is the area under the target peak divided by the total area under all peaks.
For research grade peptides, the floor is typically 95 percent. Most reputable suppliers ship at 98 percent or higher. Below 95 percent, the peptide is generally not fit for serious laboratory work. Below 90 percent, the COA itself becomes suspect.
Important: HPLC purity is mass independent. A small impurity by mass can be a large impurity by signal if it absorbs strongly at the detection wavelength. The number is useful but should be read in context with the chromatogram trace (which a good COA includes as a thumbnail image).
04 /Water and counter ion content
Lyophilized peptides are not dry. They retain bound water, and they ship as a salt (typically trifluoroacetate or acetate) bound to the basic residues. The peptide content of a lyophilized vial is the labeled mass minus water minus counter ion.
A COA reports water content (via Karl Fischer titration) and counter ion content (via ion chromatography). Typical values are 5 to 10 percent water and 5 to 15 percent counter ion. So a 5 mg vial of TFA salt peptide may actually contain 4 mg of free peptide, with the balance being water and TFA.
This matters when you reconstitute for an exact molarity. Use the net peptide content from the COA, not the labeled mass.
05 /Microbial and endotoxin limits
For research use only peptides, microbial limits and endotoxin testing are not always reported. When they are, look for total aerobic count under 100 colony forming units per gram, bacterial endotoxin under 5 endotoxin units per milligram (or per dose if specified), and no detected pathogenic species.
Lower numbers are better but more expensive to test for. If your research model involves cell culture work, endotoxin matters a great deal. If your model is purely binding assays in a tube, endotoxin matters less.
06 /Batch number and date
Every COA is for a specific batch on a specific date. The batch number on the COA must match the batch number on the product label and on your invoice. If any of the three numbers do not match, contact the supplier before you use the product.
Date matters for stability. A COA dated more than 24 months before your receipt is suspect unless the supplier has interim stability data. Most peptides are stable in lyophilized form for at least 24 months at minus 20 Celsius, but extrapolation past that point is the manufacturer's responsibility to validate.
07 /What a COA does not tell you
A COA is a snapshot of one batch at the time of testing. It is not a guarantee of future batches. It is not a statement about how a peptide will behave in any specific research model. It does not address sterility (unless explicitly stated), pyrogenicity beyond endotoxin, or genotoxicity. It does not change the research use only framing of the product.
A COA also does not validate the manufacturer. A real third party laboratory issues real COAs; a fake one issues fake ones. Look for the testing laboratory name, address, accreditation (ISO 17025 is the standard), and signature block. Cross check that the laboratory exists.
08 /What Apothify publishes
Every Apothify product page includes a link to the COA for the batch we are currently shipping. We replace the file when a new batch arrives. The link is also included in your order confirmation email. The COA is saved with your order record so you can retrieve it months later via the track page if you need it for your laboratory notebook.
If you ever receive a product and the batch on the box does not match the COA on the website, contact support@apothify.com and we will sort it out.
09 /Red flags on a COA
A COA with no laboratory name or address is meaningless. A COA with a purity reported to four decimal places (99.8742 percent) is fake; real HPLC reports two decimal places at most. A COA that cites identity by HPLC retention time alone, with no mass spectrometry, is incomplete; retention time confirms presence but not identity.
A COA that reports 100.00 percent purity should also raise suspicion. Real peptides have small impurities from synthesis. Anything above 99.5 percent is exceptional; 100 percent is a rounding artifact at best and a fake at worst.
10 /Where to go from here
Now that you can read a COA, the next practical step is to handle the peptide correctly. Continue to the storage and stability guide to learn how to keep a research peptide intact through your protocol, and to the reconstitution guide for the mechanics of preparing a working solution.
