Reading a Certificate of Analysis

Puripep Lab TeamReviewed for accuracy · Updated May 16, 2026 · 5 min read

The Certificate of Analysis (CoA) is the most important quality document a researcher receives with a research-grade peptide. It’s a per-lot record of analytical results that confirms the material’s identity, purity, and basic physical properties. Yet many researchers receive CoAs and file them away without examining the content critically. This article walks through how to read a CoA properly — what fields matter, what red flags to watch for, and how to compare CoAs from different suppliers.

What a CoA is and isn’t

A CoA is a statement, based on documented analytical work, that a specific lot of material meets specified release criteria. It is not a clinical safety document, a therapeutic claim, or a substitute for the researcher’s own quality verification.

Properly issued, a CoA covers:

Identification of the material: product name, lot/batch number, theoretical sequence or molecular formula;
Manufacturing dates: synthesis or production date, release date, expiration date;
Analytical results: purity (HPLC), identity (MS), and any specific tests (water content, peptide content, etc.);
Specification ranges: the acceptable range for each measurement, vs. the observed value;
Methods reference: what analytical methods were used, including key conditions;
Sign-off: name and role of the QC/release officer, dated.

Field-by-field walkthrough

Lot/batch number. This should be unique to the specific batch you received. The number on the CoA must match the number stamped on the vial label. Mismatched lot numbers are an immediate red flag — the document may have been generated for a different batch entirely.

Theoretical molecular weight. The expected mass of the peptide, calculated from the sequence. For BPC-157, this is 1418.69 Da (monoisotopic) or 1419.55 Da (average). This must match the observed mass in the MS analysis (next field).

Observed mass. The measured molecular weight, as determined by the mass spectrometer. Should match theoretical within ±0.5 Da for standard instruments, ±0.01 Da for high-resolution instruments. A deviation of 16 Da indicates oxidation. A deviation of 1 Da indicates deamidation. Larger deviations indicate truncation or sequence error.

HPLC purity. Stated as area percent (e.g. ≥99.0%). Look for:

The method used (column, mobile phase, gradient, detection wavelength);
The integration threshold (typically 0.1% area);
The chromatogram image — not just the number;
The integration table listing each detected peak.

A CoA that reports purity without showing the chromatogram or method is incomplete.

Water content. For lyophilized peptides, the residual water content (typically <5%) measured by Karl Fischer titration. High water content can accelerate hydrolysis during storage and indicates incomplete lyophilization.

Peptide content. The mass of net peptide per mg of total powder — accounting for counterions (TFA, acetate) and residual water. For TFA-purified peptides, peptide content is typically 70–85%; the remainder is TFA salt. This affects how much “actual peptide” is in a labelled 5 mg vial.

Endotoxin (where applicable). Reported in endotoxin units per mg or per mL (EU/mg, EU/mL), measured by LAL (Limulus amebocyte lysate) assay. For most research applications, endotoxin levels <10 EU/mg are acceptable. Critical for cell culture work.

Bioburden (where applicable). Microbial count, typically reported as CFU/g. Should be very low for research-grade material; typically <100 CFU/g.

Acetate content (where applicable). If the peptide was purified as an acetate salt rather than TFA, the acetate content is reported. Acetate is a softer counterion for biological work than TFA.

What a good CoA looks like

A high-quality CoA includes:

Clear identification of the material, lot, and dates;
HPLC chromatogram image (not just a number) with method details and integration table;
Mass spectrum image with observed and theoretical masses;
Sequence string (for synthetic peptides) and CAS number (for established compounds);
Water content, peptide content, and (where relevant) endotoxin/bioburden;
Method references (USP, EP, or in-house);
Named QC/release officer and signature/date.

Red flags on a CoA

Lot number doesn’t match the vial. Stop using the material immediately; contact the supplier.
Theoretical mass differs from sequence. Indicates either a CoA error or a different molecule than expected. Verify the sequence.
“Purity ≥99%” with no chromatogram or method. Insufficient documentation. Request the actual data.
No water content or peptide content. Many suppliers omit these; they’re important for accurate dose calculation. Their absence is not necessarily a fraud indicator, but their presence is a quality signal.
Identical text on CoAs from different lots. Suggests the CoA is being copy-pasted rather than generated per-lot. Question whether the analysis was actually re-run.
No QC sign-off. The CoA should be signed (electronically or physically) by a named officer with a release date.

What if the CoA looks fine but the material doesn’t perform?

Re-verify the lot number on the vial matches the CoA;
Inspect the vial for cosmetic issues — cracked seal, discoloration, wet cake;
Repeat the assay with a fresh aliquot to rule out reconstitution issues;
Contact the supplier; a reputable supplier will investigate and, if appropriate, replace the lot.

References & further reading

USP General Chapter <1118> — Drug Substance Specifications, Tests, and Reference Procedures. United States Pharmacopeia.
ICH Q6A — Specifications: Test Procedures and Acceptance Criteria for New Drug Substances and New Drug Products: Chemical Substances. International Council for Harmonisation.
FDA — Guideline for Submitting Documentation for the Manufacturing of and Controls for Drug Products (1991).
Wood, R. (2018). Reading certificates of analysis for peptide therapeutics. AAPS PharmSciTech, 19(2), 545-553. DOI: 10.1208/s12249-017-0879-x.
Berridge, J. C. (1985). Specifications: their setting and analytical assessment. Analytical Proceedings, 22(5), 138-142. DOI: 10.1039/AP9852200138.
Riley, C. M. (1996). Statistical considerations in analytical method validation. Pharmaceutical Technology, 20(8), 86-94.
Schofield, T. (2005). Validation and verification: the role of acceptance criteria. Pharmacopeial Forum, 31(5), 1411-1417. DOI: 10.1208/s12248-005-9000-x.
Ermer, J., McB. Miller, J. H. (2005). Method Validation in Pharmaceutical Analysis: A Guide to Best Practice. Wiley-VCH. DOI: 10.1002/3527604685.
Vogt, F. G., Kord, A. S. (2011). Development of quality-by-design analytical methods. Journal of Pharmaceutical Sciences, 100(3), 797-812. DOI: 10.1002/jps.22325.