How to Read a Certificate of Analysis (COA) for Peptides

What Is a Certificate of Analysis?

A Certificate of Analysis (COA) is a quality control document provided by a peptide manufacturer that details the identity, purity, and composition of a specific batch of peptide. For researchers, the COA is the primary tool for verifying that a purchased peptide meets the quality standards required for reliable research. Every reputable peptide supplier should provide a COA for each product, and researchers should always review it before using a peptide in any experiment.

HPLC Purity Analysis

High-Performance Liquid Chromatography (HPLC) is the gold standard method for determining peptide purity. The COA should include an HPLC chromatogram showing a single dominant peak representing the target peptide. The purity percentage is calculated from the area under this peak relative to all detected peaks. For most research applications, a purity of 98% or higher is considered research-grade, while 95-97% may be acceptable for preliminary studies.

• 98%+ purity: Research-grade, suitable for most in vitro and in vivo studies
• 95-97% purity: Acceptable for screening and preliminary research
• Below 95%: Generally not recommended for quantitative research

Mass Spectrometry (MS) Verification

Mass spectrometry confirms the molecular identity of the peptide by measuring its molecular weight. The COA should show an observed molecular weight that closely matches the theoretical (expected) molecular weight of the target peptide. Small deviations (within 0.1% of the expected mass) are typically acceptable and result from measurement precision. Larger deviations may indicate an incorrect sequence, modifications, or contamination.

For example, if you purchase BPC-157 with a theoretical molecular weight of 1,419.53 Da, the observed mass on the COA should be within approximately 1.4 Da of this value. A result of 1,419.6 Da would be acceptable, while a result of 1,425.0 Da would warrant further investigation.

Amino Acid Sequence Verification

Some COAs include amino acid analysis or sequencing data that confirms the peptide has the correct sequence. This is particularly important for longer peptides where synthesis errors (deletions, insertions, or substitutions) are more likely. While not all COAs include this level of detail, it adds an additional layer of confidence in the product identity.

Additional Quality Indicators

Beyond purity and identity, look for the following on a comprehensive COA: appearance (physical description of the lyophilized powder), solubility testing results, endotoxin levels (especially important for in vivo research), residual solvent analysis, and the net peptide content. The net peptide content is particularly important because it accounts for counter-ions, moisture, and other non-peptide components. A vial labeled as 5 mg with 80% net peptide content actually contains 4 mg of active peptide.

Red Flags on a COA

Be cautious of COAs that lack batch numbers, show generic data not specific to your purchased lot, use unusually low-resolution chromatograms, or omit mass spectrometry data entirely. A legitimate COA should be traceable to a specific production batch and include original analytical data rather than templated results. If a supplier cannot or will not provide a COA, consider this a significant red flag regarding product quality.