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How to read a peptide Certificate of Analysis

A COA is a dense, technical document. Most users skim to the "purity %" line and stop there. This guide walks the nine sections in order, so by the end you can open any research or pharma-grade COA and read it the same way a QC chemist would.

Step 1 — Match the batch number

Before reading any analytical data, verify that the COA is actually about the vial in front of you. The batch number (sometimes called lot number) printed on the COA must match the one on your vial label, character for character. A COA without a batch number is not a batch-specific report — it is a generic brochure.

If the numbers do not match, the document is either recycled from another batch or sent in error. Either way, stop here and request the correct COA before using the vial.

Step 2 — Identity block: name, sequence, formula, MW

The first analytical section typically lists:

• Peptide name — e.g. "Semaglutide" or "BPC-157". Watch for typos in this field; they appear on recycled or fake COAs.
• Sequence — the single-letter amino acid code (e.g. HAEGTFTSDVSSYLEGQAAK…). Cross-check against the known sequence for the compound.
• Molecular formula — e.g. C₁₈₇H₂₉₁N₄₅O₅₉.
• Theoretical molecular weight — this is what the mass spectrometry result (Step 4) will be compared against.

For semaglutide, the theoretical MW is ~4113.6 Da. For BPC-157, ~1419.6 Da. A COA that lists a wrong theoretical MW is flagged immediately — it means the document was not written by a chemist who knows the compound.

Step 3 — HPLC purity and chromatogram

HPLC (High-Performance Liquid Chromatography) is the standard peptide purity test. The sample is pushed through a separation column; different compounds elute at different times, and a detector records each as a peak on a chromatogram.

Read the chromatogram like this:

• One dominant peak = clean synthesis. The target peptide should be the largest and sharpest feature.
• Minor peaks = impurities. Synthesis byproducts, truncated sequences, oxidation products.
• Purity % = (main peak area ÷ total peak area) × 100. Research grade should be > 98%; pharma grade > 99.5%.

Step 4 — Mass spectrometry identity confirmation

HPLC tells you how pure the sample is. Mass spectrometry tells you what it is. The instrument measures the molecular weight of the compound and compares it against the theoretical value listed in Step 2.

A valid mass-spec result for semaglutide should measure ~4113.6 Da, within ±0.5–1 Da tolerance. If the measured mass is significantly different, the vial does not contain semaglutide — regardless of what the HPLC says about purity. HPLC can show a clean sample of the wrong molecule.

Common MS techniques on peptide COAs:

• ESI-MS — most common; produces multiply-charged ion series that deconvolute to the MW.
• MALDI-TOF — singly-charged ions; used for larger peptides.
• LC-MS — chromatography-coupled; purity and identity in one measurement.

Step 5 — Water content (Karl Fischer)

Lyophilized peptides always retain some water. Karl Fischer titration measures it to a fraction of a percent. This matters because water content subtracts from the mass of actual peptide in the vial — a 5 mg vial at 10% water contains only 4.5 mg of peptide.

Step 6 — Endotoxin (LAL) and heavy metals

For injectable peptides, endotoxin and heavy metals testing are meaningful safety metrics — not optional extras.

Endotoxin (LAL assay). Detects bacterial pyrogens at sub-nanogram levels. Results are in EU/mg. Pharma grade: < 1 EU/mg. Research grade: < 10 EU/mg is a typical ceiling. Missing endotoxin data on an injectable COA is a gap worth asking about.

Heavy metals. Residual lead, arsenic, cadmium, mercury from synthesis reagents. Pharma-grade COAs test; research-grade often skip. For chronic injectable use, presence of heavy metals data is a positive quality signal.

Step 7 — Verify the testing laboratory

Every COA should name the lab that performed the testing, the analyst, and the test dates. Verify:

1. The lab exists as a real organization you can find online.
2. The analytical dates are after the manufacturing date (not before — that would mean the data predates the batch it describes).
3. Ideally, the lab is third-party — independent of the vendor. Common third-party labs for peptides include Janoshik Analytical, EAG Labs, Intertek, and SGS.

Vendor-in-house COAs are not automatically fake — most reputable research suppliers issue their own. But a third-party COA is a stronger quality signal. If you care about verification, ask vendors if they will provide a third-party test for an additional fee. Many will.

Quick-reference checklist

Frequently asked questions

What is the first thing to check on a peptide COA?

The batch number. It must match the vial label. Everything else is secondary — if the COA does not describe your vial, the analytical data is irrelevant.

What is a good HPLC purity for a research peptide?

Greater than 98% is the research-grade standard. Pharmaceutical-grade compounds are typically > 99.5%. Below 95% raises quality-control questions regardless of price.

Can a peptide be high-purity but still be the wrong compound?

Yes. HPLC purity only measures how uniform the sample is, not what it is. Mass spectrometry confirms identity. Always check both — a 99% pure batch of the wrong molecule is still the wrong molecule.

Is an in-house vendor COA acceptable?

Usually yes for research-grade, as long as the lab methodology is documented. But third-party COAs from independent labs (Janoshik, EAG, Intertek) are a stronger quality signal and easier to verify.

What if the vendor cannot provide a COA?

That is a hard stop. A vendor that cannot produce a batch-specific COA for a peptide they are selling has no documented evidence of what is in the vial. Do not proceed.

Related COA guides

Educational use only. This guide is for research and informational purposes. It is not medical, legal, or regulatory advice. Always follow applicable laws regarding peptide acquisition and use in your jurisdiction.