How to Read a Certificate of Analysis (COA)

A legitimate peptide COA should include: the compound name and sequence (or catalog number), the batch or lot number, the date of analysis, the testing laboratory's name and contact information, the analytical methods used, and the specific results for each test. A COA that omits the testing lab's identity, lacks a batch number traceable to a specific production run, or reports only a single purity figure without the underlying chromatogram data should be treated with caution.

Third-party testing, where an independent laboratory (not the manufacturer) performs the analysis, is considered the gold standard in the research peptide industry. Labs such as Janoshik Analytical in the Czech Republic and several accredited US-based labs are frequently used for this purpose. Third-party COAs are more credible than in-house ones because the testing laboratory has no financial incentive to report favorable results.

When evaluating a supplier, researchers should verify that the COA's batch number matches the product they received, that the testing date is plausible for the production timeline, and that the reported values are internally consistent. A purity value of 99.8% paired with a mass spec trace that shows multiple significant peaks, for example, would be internally inconsistent and worth investigating.

High-performance liquid chromatography (HPLC) is the standard method for measuring peptide purity. In reversed-phase HPLC (RP-HPLC), the sample is injected into a column packed with a hydrophobic stationary phase and eluted with a gradient of increasing organic solvent concentration. Different compounds spend different amounts of time interacting with the stationary phase (this is the retention time), so they elute at different points and can be quantified independently.

The purity percentage reported on a COA represents the target compound's peak area as a fraction of the total area of all peaks detected. For example, if the target peptide's peak represents 97.2% of the total UV absorbance area in the chromatogram, the HPLC purity is reported as 97.2%. The remaining 2.8% consists of minor impurities: deletion sequences (peptides that are missing one or more amino acids due to incomplete coupling steps in synthesis), oxidized forms, and other synthesis-related byproducts.

A purity of 95% or above is generally considered research-grade for most laboratory applications. Purity above 98% is common for high-quality suppliers and is important for sensitive assays where minor impurities could confound results. Researchers should be aware that HPLC purity as measured by UV absorbance at 220 nm does not perfectly represent the mass fraction of the target compound because different molecules absorb UV light with different efficiencies.

The chromatogram itself (the actual graph of absorption versus time) provides more information than the summary percentage. Researchers should examine the chromatogram to confirm that the main peak is well-resolved from any minor peaks, that there are no suspicious broad or tailing peaks that might indicate polymeric aggregates, and that the baseline is flat and stable.

While HPLC tells us how pure a sample is, mass spectrometry (MS) tells us what it is. MS measures the mass-to-charge ratio (m/z) of ionized molecules, allowing the researcher to determine the molecular weight of the compound with very high precision. For a peptide, the molecular weight can be calculated from the amino acid sequence, and comparing the theoretical molecular weight to the observed MS value confirms (or refutes) identity.

Most COAs report results from electrospray ionization mass spectrometry (ESI-MS) because it is gentle enough to preserve large molecules like peptides without fragmenting them. In ESI-MS, multiply-charged ions are commonly formed, so the spectrum typically shows a series of peaks at m/z values corresponding to [M+H]+, [M+2H]2+, [M+3H]3+ and so on. The molecular weight is calculated from any of these observed peaks using the known charge states.

A positive identity confirmation is reported as the observed molecular weight matching the theoretical molecular weight within a defined tolerance, typically 0.5 Daltons or less for peptides in the 1000-5000 Da range. Some COAs also report percentage purity by mass spectrometry, which can differ from the HPLC purity figure because MS detection efficiency varies by compound chemistry.

A COA that provides only HPLC purity and lacks any mass spectrometry confirmation should be viewed as incomplete. It is possible for a sample to show high HPLC purity while containing a related compound of similar polarity, such as a scrambled sequence or a modified form of the target peptide, that would only be distinguished by mass-based identity confirmation.

Janoshik Analytical is a Czech Republic-based laboratory that has become a recognized third-party testing resource in the research peptide community. Their reports typically include an RP-HPLC chromatogram with the calculated purity percentage and an ESI-MS spectrum with the observed and theoretical molecular weight comparison. The report also includes the sample identification (usually submitted by the client as a code, not the compound name), the analyst's signature or initials, and the date.

When reading a Janoshik report, look for the sample ID to match what the supplier has provided, the HPLC purity to be clearly stated (typically in the 95-99%+ range for reputable suppliers), and the mass spectrum to show a clear major peak (or set of multiply-charged peaks) corresponding to the expected molecular weight. The report's issue date should predate or closely match the product batch date.

Other accredited labs, including US-based ISO 17025-certified laboratories, provide COAs that follow a similar structure but may present data in different formats. ISO 17025 accreditation indicates that the laboratory has been assessed for technical competence and quality management by an independent accreditation body, which is a meaningful quality indicator. Regardless of the lab, the key data points remain the same: HPLC purity, MS identity, and traceability to a specific batch.

Several patterns in COA documentation warrant scrutiny. A purity value that is implausibly high (for example, 99.9%+ for a complex peptide with multiple reactive functional groups) without supporting chromatographic evidence may indicate fabricated data. A COA from a testing lab that cannot be verified to exist or that lacks a physical address and contact information is another warning sign.

Reused COAs, where the same document is applied to multiple batches without updating the batch number or date, are unfortunately not uncommon in low-quality supply chains. Researchers should request batch-specific documentation and cross-reference the reported batch number against the product label. Some suppliers publish COAs on their product pages; for high-stakes research, requesting the original file directly from the testing laboratory is the most reliable verification method.

Finally, be aware that a passing COA indicates purity and identity at the time of testing. It does not guarantee that the material was stored, shipped, and handled correctly between testing and receipt. Visual inspection of the lyophilized material (it should be a fine, dry white powder free from discoloration or clumping) and attention to the cold chain documentation are complementary quality checks.