How to read a peptide certificate of analysis

A peptide COA is a batch-specific analytical report that answers three questions about a lyophilised powder: is it the right molecule, how clean is it, and how much of the powder is peptide. Bachem, a large peptide manufacturer, frames quality control around the same questions: whether the powder is the desired product, how pure it is, what by-products it contains and how high the product content is. ^[1] Each question needs its own method. The United States Pharmacopeia's work on peptide reference standards uses mass spectrometry, NMR and chromatography for identity, and HPLC and GC methods for peptide content and impurities. ^[7]

The batch is the unit that matters. Synthesis and purification vary from run to run, and Bachem notes that purity can differ from batch to batch. ^[1] A generic PDF for "BPC-157" tells you about some batch, somewhere. A certificate tied to the batch number printed on your vial tells you about the powder in your hand.

At Peptides Collective, an independent lab tests every batch before it goes on sale, for purity by HPLC and identity by mass spectrometry. The certificate is published in our certificate of analysis library under the batch number printed on the vial, and our testing page explains how a batch moves from test to sale.

Every line on a COA either identifies the sample or reports a measured result, and the header lines matter as much as the numbers. Read them in the order below.

Bachem lists the methods behind the optional lines: water content by Karl Fischer analysis, residual solvents by gas chromatography, and acetic acid or trifluoroacetic acid (TFA) by HPLC or ion chromatography. ^[1] Those counter-ions come from synthesis. Solid-phase synthesis relies on TFA for cleavage and purification, so peptides are commonly obtained as TFA salts. ^[8] Salt and water add weight to the powder without adding peptide.

A worked example, line by line

The certificate below is illustrative. The figures are invented for teaching and come from no real batch or lab.

The identity line passes, because both ions point to the same neutral mass (the arithmetic is in the next section). The purity line tells you the peptide-related signal is dominated by one peak. The content line changes the answer to "how much BPC-157 is in the vial": if 5mg is the powder weight, the target peptide is about 5 x 0.80 x 0.985 = 3.9 mg. If 5mg is the declared peptide weight, the certificate should report an assay against that label claim. The BPC-157 product page (5mg, A$81) links the certificate for the current batch.

The mass spectrometry line confirms identity when the observed ions convert back to the compound's known mass. Electrospray ionisation, the usual method for peptides, typically yields multiple charge values for each molecular mass, while MALDI spectra typically contain singly charged ions. ^[4] An ion carrying z extra protons appears at m/z = (M + z x 1.00728) / z, where M is the neutral mass.

That formula lets you check any certificate. Take M from PubChem, calculate the expected ions and compare.

The masses come from PubChem for BPC-157 ^[3] and tirzepatide. ^[9] We calculated each ion with a proton mass of 1.00728.

Three habits make the check reliable:

1. Know which mass the lab used. Monoisotopic mass counts only the most common isotopes. Average mass weights all of them. For tirzepatide the two differ by about 2.5 units, so a report of 4810.5 and a PubChem entry of 4813 can both be correct.
2. Look for agreement across charge states. Two or three ions that convert to the same neutral mass are stronger evidence than one number that happens to fit.
3. Read differences as clues. Oxidation, deletion of an amino acid and leftover protecting groups are known peptide impurities, and each changes the mass. ^[10] A result several units away from both the average and monoisotopic value needs an explanation from the lab.

Mass spectrometry has one blind spot worth knowing. Racemisation during synthesis produces diastereomeric impurities, ^[10] and these have the same mass as the target. USP scientists note that chiral or isobaric amino acids may need additional techniques for full characterisation. ^[7] A clean mass result confirms the formula. It cannot confirm every stereocentre.

For tirzepatide in 10mg and 20mg vials, from A$98, the ions to look for sit near m/z 1203.6 to 1204.3 (4+) and 963.1 to 963.6 (5+).

The acceptable purity depends on the experiment, and a figure only means something alongside its method. Bachem, which sells peptides by grade, recommends above 95% for NMR, crystallography and peptides used as references in quantitative studies, 90 to 95% for quantitative enzyme and receptor studies, above 80% for qualitative work such as Western blotting, and above 65% (immunograde) for raising polyclonal antibodies. ^[1]

Two cautions sit behind every percentage.

Purity is a ratio of UV peaks. Bachem defines HPLC purity as the area of the main peak in relation to the total area of all peaks, typically read at 210 to 220 nm. ^[1] Anything that does not absorb there is missed. A 2020 study found undeclared mannitol at 20% and 43% w/w in two commercially sourced custom peptides; the authors describe LC-based quality control as potentially "blind" to impurities of this kind and found the mannitol by NMR. ^[2]

A high number on a label proves nothing on its own. Independent tests of online products show the gap between claims and measurements:

• Three semaglutide vials bought from illegal online pharmacies measured 7.7% to 14.37% purity against 99% claimed on the labels. Endotoxin was detected in all samples, at 2.1645 to 8.9511 EU/mg. ^[11]
• Melanotan II vials from three online shops held 4.32 to 8.84 mg against 10 mg claimed, and two shops' vials contained unknown impurities of 4.1% to 5.9%. ^[12]

Both studies used liquid chromatography with mass spectrometry, the methods a good COA reports, run by independent academic labs.

The amount of target peptide in a vial is the powder weight multiplied by the net peptide content and, for peptide-related impurities, the purity. Purity and net content answer different questions. Bachem defines net peptide content as the percentage of peptide relative to non-peptide material, mostly counter-ions and moisture, and states that net peptide content and purity are not equivalent. Peptides rich in basic amino acids can show a low net content even when extremely pure, because they form salts. ^[1] Peptide drugs often exist as salts with different counter-ions. ^[13]

The 2024 semaglutide study shows how far apart the numbers can sit. One vial contained 50.1 mg of powder, carried a label amount of 3 mg and held a measured 3.86 mg of semaglutide. That is 28.56% more peptide than the label, and a measured purity of 7.7%, because the rest of the powder was something else. ^[5] Both statements about the same vial are true. The label described peptide weight, and the powder carried bulk the label never mentioned.

Run the arithmetic on any certificate with the three figures it gives you:

These rows are illustrative arithmetic. A content figure near 100%, such as 95 to 105%, reads as an assay against the label claim, where the label already states peptide weight. A figure of 60 to 85% reads as a share of the powder. Ask the lab which one it means before you compare two certificates. Net content feeds directly into concentration when you reconstitute for lab work, which our guide on how to reconstitute peptides works through in mg per mL.

A COA is genuine when the lab that issued it confirms the report exists and describes the same batch as your vial. Everything else is supporting evidence. Work through these checks in order.

A few of those checks rest on public registers. In many countries, ISO/IEC 17025 is the standard against which laboratories are accredited as technically competent for the methods on their scope, and NATA notes that suppliers and regulators often reject results from unaccredited labs. ^[14] Accreditation covers listed methods, so check the scope as well as the logo. ABN Lookup shows whether an Australian business's ABN is active or cancelled, and a cancelled status means the business has ceased trading. ^[15]

Lab-side verification is the strongest single check. Some testing labs offer a verification page, or a QR code on each report, that returns the original. If a certificate names a lab with no such system, email the lab with the report ID and batch number.

The label check has a legal side. The TGA calls unmarked vials, code-only labels and missing ingredient information major red flags, and says such vials will not be released under the Personal Importation Scheme. ^[16]

A COA covers the tests listed on it, for one sample, on one date, and nothing else. The gaps are predictable:

• Sterility and endotoxin. HPLC and MS say nothing about microbes or bacterial endotoxin. Endotoxin is measured separately, usually by the Limulus amebocyte lysate (LAL) bacterial endotoxins test, and even that assay has documented low-recovery problems in some samples. ^[17] In the semaglutide study, the powders held no viable microorganisms at testing, yet endotoxin was present in every sample. ^[11]
• UV-transparent material. Sugars, salts and water escape a UV purity figure, as the mannitol findings showed. ^[2]
• Same-mass isomers. Diastereomers from racemisation pass a mass check. ^[10]
• Time after testing. The report describes the powder on the test date. Storage and shipping come later; our guide on how to store peptides covers temperature, light and moisture for lyophilised vials.
• Legal and sport status. A perfect certificate changes no schedule. BPC-157 is in Schedule 4 and in Appendix D clause 5 of the June 2026 Poisons Standard, which makes possession without authority an offence, and tirzepatide is in Schedule 4. ^[6] WADA's 2026 List names BPC-157 in class S0, prohibited at all times. ^[18] Our guide to whether peptides are legal in Australia sets out the status of every compound we stock.
• Regulatory approval. The TGA says "research use only" and "not for human use" disclaimers do not change whether a product is regulated as a therapeutic good. ^[19] The TGA also warns that unapproved peptide products may contain the wrong active ingredient or significantly more or less than the label states. ^[20] A certificate is the tool that tests that claim for one batch.

Read a peptide COA as three linked measurements: mass spectrometry for identity, HPLC for peptide-related purity and net content for how much of the powder is peptide. Check the numbers against PubChem and the vial label, then confirm the report with the lab that issued it. A certificate that passes all of this tells you what is in one batch; the Poisons Standard, the TGA and the WADA List still govern everything else.