Understanding Certificates of Analysis
How to read a CoA, what HPLC purity figures mean, and why mass spectrometry confirmation is essential for reproducible research outcomes.
A Certificate of Analysis (CoA) is the primary quality document for any research compound. It records the results of analytical testing performed on a specific batch, giving you the evidence you need to assess whether a compound meets your research requirements before you use it. Knowing how to read and interpret a CoA is an essential skill for any researcher working with synthetic peptides.
What a CoA contains
A well-structured CoA will include: the compound name and sequence, the batch or lot number, the date of manufacture and testing, the analytical methods used, the results of each test, and the name of the testing laboratory. For research peptides, the two most important analytical results are the HPLC purity figure and the mass spectrometry identity confirmation. Some CoAs also include additional data such as water content (Karl Fischer titration), residual solvent levels, or endotoxin testing depending on the intended application.
Reading HPLC purity data
High-Performance Liquid Chromatography (HPLC) separates the components of a sample based on their chemical properties as they pass through a column under high pressure. The detector — typically a UV detector set at 214 nm or 220 nm — measures the absorbance of each component as it elutes. The result is a chromatogram: a graph of detector response over time. Each peak represents a component in the sample. Purity is calculated as the area of the main peak divided by the total area of all peaks, expressed as a percentage. A purity of ≥99% means that 99% or more of the UV-absorbing material in the sample is the target peptide.
What HPLC purity does not tell you
HPLC purity is a relative measurement — it tells you what proportion of the sample is your target compound, but only among UV-absorbing species. Compounds that do not absorb UV light (such as certain salts or residual solvents) will not appear in the chromatogram and therefore will not affect the purity figure. This is why HPLC purity should always be considered alongside other quality data, and why sourcing from suppliers who use accredited independent laboratories matters.
Mass spectrometry identity confirmation
Mass spectrometry (MS) confirms that the compound in the sample is the compound you ordered. The technique ionises the sample and measures the mass-to-charge ratio (m/z) of the resulting ions. For a peptide, the observed molecular weight should match the theoretical molecular weight calculated from the amino acid sequence. A discrepancy would indicate a sequence error, modification, or contamination. Most CoAs for research peptides report MS data as the observed [M+H]+ or [M+2H]2+ ion, which should match the theoretical value within a small tolerance (typically ±0.5 Da for ESI-MS).
Third-party vs. in-house testing
A CoA is only as trustworthy as the laboratory that produced it. In-house testing by the manufacturer creates a conflict of interest — the same organisation that profits from selling the compound is also certifying its quality. Independent third-party testing by an accredited analytical laboratory removes this conflict. When evaluating a supplier, ask whether their CoAs are produced by independent laboratories and whether the raw data (chromatograms, spectra) is available on request. At Peppy, all batch testing is performed by accredited third-party laboratories and CoAs are published for every batch.
Batch-specific documentation
CoAs are batch-specific documents. A CoA issued for batch 001 does not apply to batch 002, even if the compound is nominally identical. Always verify that the CoA you are reviewing corresponds to the specific batch you have received. The batch or lot number on the CoA should match the number on the product label. If you receive a product without a matching CoA, contact the supplier before using the compound in your research.