A Certificate of Analysis (CoA) is not optional documentation. It is the only verifiable evidence that the vial in your freezer matches the molecule on the label. Yet most researchers skim them. This decoder walks through every line you should be reading, and what each value tells you about the batch.
1. Batch number and date
The CoA must reference the specific batch shipped to you. A supplier-wide template is a red flag — it means you are looking at marketing material, not analytical data. The date on the CoA should be within a few months of dispatch, ideally within the last 90 days for sensitive sequences.
2. HPLC chromatogram and purity percentage
Reverse-phase HPLC separates the target peptide from impurities and reports purity as a percentage of total peak area. Look for:
- A single dominant peak at the expected retention time (typically 5–15 minutes for short peptides)
- Purity ≥98% — anything lower introduces unknown variables
- A clean baseline with minimal noise
- No prominent secondary peaks adjacent to the main peak (indicates deletion sequences or oxidation)
3. Mass spectrometry — molecular weight confirmation
Mass spec confirms that the peak you measured is actually the molecule you ordered. Look for the observed mass within ±0.5 Da of theoretical for short peptides, ±2 Da for longer sequences. A mass deviation outside that range indicates incorrect synthesis or post-synthetic modification (oxidation, deamidation).
4. Water content (Karl Fischer titration)
Lyophilised peptides retain bound water that affects net peptide mass. Karl Fischer titration measures water content as a percentage. Expect 4–10% for properly lyophilised material. Higher water content means less peptide per vial than the label suggests — directly affects your reconstitution math.
5. Peptide content (net peptide assay)
Net peptide content is the percentage of the vial mass that is the actual peptide, after subtracting counter-ions (TFA, acetate), water, and other residuals. Expect 75–90% for most lyophilised research peptides. The CoA should report this explicitly — if it does not, the supplier is leaving you to guess.
6. Counter-ion content
Peptides synthesised by solid-phase peptide synthesis (SPPS) are typically purified by ion exchange, leaving residual TFA or acetate counter-ions. The CoA should report counter-ion type and percentage. TFA exposure at high concentrations affects cell-based assays — acetate exchange is preferred for sensitive in vitro work.
7. Appearance and solubility notes
White to off-white lyophilised cake is standard. Yellowing indicates oxidation. The CoA should note solubility in standard solvents (water, DMSO, acetic acid) — this saves trial-and-error during reconstitution.
8. Storage and shelf-life statement
Recommended storage conditions and expiry date should be on every CoA. Standard recommendation: lyophilised peptide at –20°C in sealed vial, protected from light, stable for 12–24 months depending on sequence.
The single-page sniff test
A complete CoA fits on one page and contains: batch number, synthesis date, HPLC chromatogram with purity percentage, mass spectrum with observed/theoretical masses, water content, peptide content, counter-ion data, appearance, solubility notes, and storage recommendation. Missing any of those means the supplier is not running a full QC protocol — or is hiding the data.
Chempeptides publishes batch-specific CoAs on every product page. Browse the research catalogue to inspect current batches before you order.
Research use only.