A certificate of analysis (CoA) is the lab report for one lot of one compound. It should name the compound, the lot number, the test date and the laboratory, and it should match the lot printed on your vial. A CoA without a lot number, or a single CoA reused across many lots, tells you little.
Purity by HPLC
Reversed-phase HPLC separates the target peptide from truncated sequences, deletion products and oxidised variants. Purity is reported as the area of the main peak divided by the total peak area, typically at 214 or 220 nm where the peptide bond absorbs. A value of 99.2% means the main peak accounted for 99.2% of what the detector saw. Look for the chromatogram itself: a sharp main peak with small, well-separated impurities is what a clean synthesis looks like.
Identity by mass spectrometry
HPLC purity says the sample is mostly one thing; mass spectrometry says what that thing is. The CoA lists a theoretical mass (calculated from the sequence) and an observed mass. For BPC-157 the theoretical monoisotopic mass is about 1418.7 Da and the average molecular weight is 1419.5 g/mol; an observed value within roughly 0.1% confirms identity. Multiply-charged ions ([M+2H]2+, [M+3H]3+) are normal for larger peptides and are converted back to the neutral mass on the report.
Appearance and water content
Lyophilized peptides are usually white to off-white powders or cakes; GHK-Cu is blue because of the copper complex. Water content (Karl Fischer) and residual solvent lines, where present, indicate how thoroughly the lot was dried.
Counter-ion and net peptide content
Peptides are purified in acidic mobile phases and are isolated as salts, most often trifluoroacetate (TFA) or acetate. The counter-ion, bound water and any excipient add to the gross weight of the powder, so the net peptide content of a vial is typically 70–90% of its gross mass. Reputable suppliers fill vials to a labeled peptide mass, not a gross mass. See net peptide content for the arithmetic.
What is not on a research CoA
Sterility, endotoxin and pyrogen testing are pharmaceutical release tests. They may appear on some research CoAs but are not standard, and their absence is a reminder of what the product is: a chemical reagent for laboratory use.