Auditing a COA Line by Line

The COA should prominently name the laboratory that performed the analysis. This means a real business name, a physical address, and ideally a contact method. It is not the supplier's name — it is the independent testing facility.

If the issuing entity is the same as the seller, or if no third-party laboratory is named anywhere on the document, the COA is self-issued. A self-issued COA cannot verify the material because the issuing party has a commercial interest in the result.

The lot or batch number on the COA must exactly match the lot number on the vial or product label you would receive. This is the chain-of-custody linchpin. A COA with no lot number, a different lot number, or a placeholder is not a certificate for the material being supplied — it is a certificate for something else.

Some sellers attach a generic COA that covers a compound in general, without reference to a specific batch. This practice is common, and it is a disqualifying flaw. A generic COA does not verify any specific batch of material.

The analysis date should be close to the manufacture date of the batch. A certificate dated years before the supplied material was synthesised was not generated for that material. Similarly, the analyst who performed the testing should be identifiable — through a signature, printed name, or laboratory stamp — creating accountability for the results.

The purity figure is calculated as the area of the main peak divided by the total peak area, expressed as a percentage. For research-grade synthetic peptides, purity is commonly expected at ≥98% by HPLC. Values below this indicate a higher proportion of impurities — truncated sequences, protecting-group residues, or synthesis by-products.

A purity of 95–97% may be acceptable for some applications but should be understood as less pure. A purity below 90% represents a substantially impure batch that requires context and judgement about fitness for purpose.

The chromatogram is the actual evidence of the purity figure. It shows a plot of UV absorbance over time (retention time on the x-axis, absorbance on the y-axis). A high-purity peptide will show one dominant, well-resolved peak — the target compound — with minor peaks or a flat baseline elsewhere. The area under the main peak should correspond closely to the stated purity.

When reading a chromatogram, look for: the retention time of the main peak (the target compound), clear integration markers showing where the peak area was measured, the absence of large unresolved peaks or shoulders adjacent to the main peak, and a stable baseline before and after elution.

A poorly resolved peak with shoulders may indicate co-eluting impurities that are not counted separately. A rising or noisy baseline may indicate matrix effects or instrument issues. These are not automatic disqualifications, but they warrant closer scrutiny of the purity figure.

For a given peptide, the exact molecular weight can be calculated from its amino acid sequence and modifications. The mass spectrometer reports the found mass, usually as the monoisotopic mass or the average molecular mass. The COA should present both values side by side.

Peptides are multiply charged in electrospray ionisation (ESI), the most common technique for LC-MS of peptides. A peptide with a molecular weight of 3000 Da might appear at m/z 1501 as a doubly charged [M+2H]²⁺ species, or at m/z 1001 as a triply charged [M+3H]³⁺ species. The stated molecular weight should be derivable from the reported m/z values and charge states. A COA that reports only m/z without the calculated molecular weight requires the reader to perform this conversion, which is acceptable but less transparent.

Like the HPLC chromatogram, the mass spectrum is the raw evidence. It should show the observed ion peaks, clearly labelled with their m/z values, and ideally with the charge states identified. The most abundant ion series should correspond to the expected compound.

A spectrum that shows only one dominant set of ions corresponding to the target peptide is straightforward to interpret. A spectrum cluttered with many additional ion series may indicate impurities or in-source fragmentation, and a competent analyst's interpretation note should accompany complex data.

Lyophilised peptides always carry residual water from the freeze-drying process. Karl Fischer (KF) titration is a selective electrochemical method for quantifying this water, referenced in USP general chapter <921> and European Pharmacopoeia 2.5.12. The result is expressed as water (% w/w).

The significance is practical: a peptide vial nominally containing 10 mg with a water content of 10% actually contains only 9 mg of anhydrous peptide mass. For dose-response research, this difference matters. Water content above 15% may also indicate poor lyophilisation conditions that could accelerate degradation.

Endotoxins are lipopolysaccharides (LPS) from the outer membrane of gram-negative bacteria, produced as by-products of microbial contamination during synthesis or handling. They are heat-stable and cannot be destroyed by standard autoclave sterilisation. In cell culture or in vivo research, even small amounts of endotoxin can trigger inflammatory responses that invalidate results.

The Limulus Amebocyte Lysate (LAL) assay uses a clotting reaction from horseshoe crab blood to detect endotoxin. Results are expressed in Endotoxin Units per milligram (EU/mg). The WHO and pharmacopoeial standards for parenteral pharmaceuticals set strict endotoxin limits, but no single threshold applies universally to all research peptide applications — the relevant limit depends on the experiment and species involved. What a COA must provide is the measured value so the researcher can make that determination.