How to Read a Peptide Certificate of Analysis (CoA) and HPLC Report

A peptide Certificate of Analysis (CoA) is the supplier's documentation of identity, purity, and quality. For research peptides — where there is no FDA oversight of the supply chain — the CoA is most of what stands between you and an unknown substance. Most users glance at the purity number and move on. Here's how to actually read the document.

What a complete CoA includes

A legitimate research-grade peptide CoA contains, at minimum:

1. Product identity — peptide name, sequence, molecular formula, molecular weight
2. Lot number and manufacturing date
3. HPLC purity — typically reported as a percentage with the chromatogram attached
4. Mass spectrometry — confirmation of molecular weight matching expected
5. Water content (Karl Fischer or thermogravimetric analysis)
6. Counterion content (typically acetate, sometimes TFA)
7. Visual inspection notes — appearance, color
8. Test method references — which HPLC column, mobile phase, detector
9. Date of analysis and analyst signature (or lab certification)

If your CoA is a single-page summary with no chromatograms, no mass spec data, and no testing methodology — that's not a CoA, it's marketing.

HPLC purity: the headline number and the chromatogram

HPLC (High-Performance Liquid Chromatography) separates the peptide from impurities and reports each peak as a percentage of total area. The "98% purity" headline is the percentage of the main peak relative to all detected peaks.

What to read on the actual chromatogram:

• The main peak should be sharp and well-resolved — a wide, asymmetric peak suggests poor synthesis or degradation.
• Look at impurity peaks. A 98% main peak with a single 1.5% impurity is different from a 98% main peak with twelve 0.16% impurities. The first suggests one specific synthesis byproduct; the second suggests poor overall synthesis.
• The retention time should match the reference standard — most CoAs include or reference an expected retention time for that peptide on the specific HPLC method used.
• Detector wavelength should be appropriate. Most peptides absorb at 220 nm (peptide bond) or 280 nm (aromatic residues — only useful if the peptide contains Trp, Tyr, or Phe). A CoA reporting purity at 254 nm for a peptide with no aromatic residues is suspicious.

A red flag: identical chromatograms across different lots or different peptides. Some vendors copy-paste chromatograms because nobody reads them. If you have access to multiple CoAs from the same vendor, compare the chromatograms; identical-looking traces are a problem.

Mass spectrometry: the identity check

HPLC tells you how pure the main peak is. Mass spec tells you whether the main peak is actually the peptide you ordered.

The MS report should show a peak matching the theoretical molecular weight of your peptide. For a 5,000 Da peptide measured by ESI-MS, the observed mass should match the theoretical mass within ~1 Da.

Important: many peptides ionize as [M+H]⁺, [M+2H]²⁺, [M+3H]³⁺, etc. The CoA should show one or more of these characteristic ions matching expected mass-to-charge ratios. If only a single mass is reported and it doesn't match the theoretical [M+H]⁺ exactly, look for the multiply charged species.

If the mass spec is missing entirely: this is the single biggest red flag on a CoA. HPLC purity without mass spec confirmation tells you the sample is "pure something" without confirming what that something is. Counterfeit peptides with completely wrong sequences can show 98% HPLC purity.

Water content: the dosing impact

Lyophilized peptide powder is hygroscopic. A vial labeled "5 mg peptide" actually contains 5 mg of dry peptide plus whatever water has been adsorbed plus the counterion (usually acetate). Water content is typically 3–10% for a well-handled peptide.

Why this matters for dosing: if you're calculating doses based on the labeled mass, a 10% water content means your effective peptide mass is 10% lower than labeled. For most off-label use this is within tolerable error, but precision matters for dose-sensitive peptides (Tesamorelin, GLP-1s).

Counterion content: the bigger correction

Most synthetic peptides are isolated as acetate salts (sometimes TFA salts from purification). The CoA should report acetate or TFA content as a percentage of total mass.

Practical example: a 10 mg vial labeled "BPC-157" might contain:

• 8.5 mg actual peptide (free base equivalent)
• 1.0 mg acetate counterion
• 0.5 mg water

If you're dosing based on labeled mass, you're overestimating peptide mass by ~15%. For some peptides this is irrelevant; for others it changes the calculation.

The correction: net peptide content = labeled mass × (1 − acetate% − water%). Quality CoAs do this calculation for you.

TFA vs acetate: a safety consideration

Trifluoroacetic acid (TFA) is used during peptide synthesis as a cleavage and protecting-group reagent. Some peptides are isolated as TFA salts because the acetate-exchange step adds cost.

TFA at injection-relevant doses isn't dangerous in any acute sense, but for peptides used long-term or at high doses, the acetate-form is preferred. Quality vendors specify which counterion their peptide is supplied as. If the CoA doesn't say, the peptide is more likely to be the cheaper TFA form.

Endotoxin and bioburden testing

Truly research-grade peptides usually don't include endotoxin testing because they're nominally not for human use. If a peptide is being used parenterally (subcutaneous, intramuscular), endotoxin contamination matters — pyrogenic reactions are possible.

Look for endotoxin testing by LAL (Limulus Amebocyte Lysate) assay, with results in EU/mg (endotoxin units per milligram). Pharmaceutical-grade peptides typically have <5 EU/mg; research-grade peptides often don't test at all.

If the vendor doesn't provide endotoxin data, you're dosing material with unknown pyrogenic risk.

Sterility testing

Lyophilized peptide is unlikely to support microbial growth in its dry state, but reconstituted peptide solutions can. Sterility testing on the lyophilized product is uncommon for research-grade material; some 503A and 503B compounding pharmacies do test reconstituted product or final fill-finish.

For research-grade powder, the practical reality is that you're providing the sterility step yourself when reconstituting with bacteriostatic water in clean conditions.

Red flags on a CoA

• No chromatogram attached (just a number)
• Identical chromatograms across lots
• Mass spec missing entirely
• No water content or counterion data
• Test date predating manufacture date (yes, this happens)
• Lot number missing or generic
• No analyst or lab identification
• Unrealistic purity claims (>99.9% for a peptide >30 amino acids is rare from any synthesis)
• Purity reported to too many significant figures ("98.7843%")
• Different peptide name on CoA than on the vial label

What you can do without a CoA

• Visual inspection — peptide should be a fluffy white or off-white lyophilized cake. Yellow/brown discoloration suggests degradation or impurity. Hard, glassy material can indicate moisture damage.
• Reconstitution behavior — should dissolve in bacteriostatic water within 30 seconds with gentle swirling. Cloudy solutions or persistent particulates suggest impurity.
• Send for independent testing — Janoshik Analytical (Czech Republic) is the most-cited independent lab for research peptide testing. Costs $20–50 per sample for HPLC/MS.

Bottom line

A peptide Certificate of Analysis is only as useful as your ability to read it. The headline purity number is the least informative part. The chromatogram, mass spec confirmation, water and counterion content, and the testing methodology all matter more. For research-grade peptides where there is no FDA oversight, the CoA is most of your quality assurance — read it carefully or send a sample for independent testing.