How to Read a Peptide Certificate of Analysis

A peptide Certificate of Analysis (CoA) is the quality passport that tells you exactly what you’re putting into your experiment.

What a Certificate of Analysis (CoA) Contains

Every time a research peptide is shipped, the supplier provides a one‑page report that records the results of laboratory tests performed on that batch. The CoA is meant to be read by scientists, quality managers, and regulators to confirm that the material meets the specifications claimed on the product label.

• Identity – usually confirmed by mass spectrometry or sequencing
• Purity – percentage of the target peptide measured by HPLC
• Impurities – list of detectable side‑products or truncated sequences
• Molecular mass – exact mass from MALDI‑TOF or ESI‑MS
• Counter‑ion and salt content – e.g., TFA, acetate, or chloride
• Water content – important for stability and accurate weighing
• Batch number, manufacture date and expiry – traceability details
• Storage instructions – recommended temperature and protection from light

Key Metrics to Look At

The most critical numbers for most researchers are the purity percentage and the mass accuracy. Purity tells you how much of the powder is the exact peptide you ordered, while mass accuracy confirms that the peptide’s molecular weight matches the expected value. Together they give confidence that the peptide will behave as reported in the literature.

• HPLC purity – usually expressed as “≥ 98 % by HPLC”; a higher value means fewer contaminant fragments.
• Mass accuracy – reported as a few parts per million (ppm) difference from the theoretical mass; values under 5 ppm are typical for high‑quality material.
• Water content – expressed as a percentage; low water (< 5 %) helps maintain stability.
• Counter‑ion type – identifies the chemical that balances the peptide’s charge; some assays are sensitive to TFA versus acetate.

Understanding Mass and Sequence Confirmation

Mass spectrometry techniques such as MALDI‑TOF (matrix‑assisted laser desorption/ionisation time‑of‑flight) or ESI‑MS (electrospray ionisation mass spectrometry) generate a spectrum that shows the exact mass of the peptide. The reported mass should match the calculated mass based on the amino‑acid sequence; a deviation of only a few ppm indicates that the peptide chain is intact and the synthesis was successful. If the observed mass differs significantly, it may signal a truncation, an unintended modification, or a synthesis error.

Other Important Information

Beyond the core analytical data, the CoA lists the batch number (for traceability), the expiry date (usually one to two years from the date of analysis), and recommended storage conditions such as “‑20 °C, protected from moisture”. It may also note the synthesis method – solid‑phase peptide synthesis (SPPS) or recombinant expression – because each route can affect impurity profiles.

Common Pitfalls and Red Flags

Not every CoA is created equal, and certain omissions or out‑of‑spec values should prompt a follow‑up with the supplier before using the material in critical experiments.

• Purity below the claimed threshold (e.g., < 95 %).
• Missing or vague impurity profile – no list of detectable side‑products.
• Mass deviation greater than 10 ppm or unexplained additional peaks.
• No reference to an independent testing laboratory.
• Expired or absent expiry date.
• Unclear storage recommendations that contradict standard peptide handling.

Questions Worth Asking When Reviewing a CoA

• Does the HPLC purity meet or exceed the ≥ 98 % benchmark for my assay?
• Is the reported mass within a few ppm of the theoretical value?
• Are impurity peaks identified and quantified, and could they interfere with my read‑out?
• Has an independent, accredited lab performed the key analyses?

Compliance reminder

All information presented here is for research and educational purposes only. Peptides listed on this site are not approved for human or animal consumption, are not listed on the Australian Register of Therapeutic Goods (ARTG), and must be used strictly under appropriate laboratory and ethical guidelines.