Table of Contents
What a COA Actually Documents
A Certificate of Analysis is a batch-specific document — it reports on a particular lot of a compound, not on the compound in general. This distinction matters: a supplier might have excellent COAs for some batches and poor-quality results for others. The lot number on your COA should match the lot number on your vial.
A complete peptide COA typically includes: compound name and sequence, lot or batch number, synthesis date or testing date, analytical test results (HPLC, MS, and optionally Karl Fischer and amino acid analysis), and the identity of the testing laboratory. When a COA omits the lot number or testing date, it cannot be matched to a specific production batch and should be treated with caution.
The lab testing page explains how Peptides Canada structures its quality documentation. Each vial is associated with a specific batch COA that includes all key analytical fields.
Reading the HPLC Section
The HPLC section of a COA reports the chromatographic purity of the compound. The most important number is the main peak area percentage — the proportion of total UV-detected area attributed to the target peptide. For research-grade material, this figure should generally be 98% or higher.
When a chromatogram image is included (as it should be in a well-formed COA), look for:
- A dominant main peak — the target compound. It should be clearly the largest peak in the chromatogram.
- Minor impurity peaks — small peaks representing synthesis by-products, truncated sequences, or reagent residuals. Their aggregate area should correspond to the impurity percentage.
- Baseline resolution — peaks should be distinct, not fused. A single broad peak that is reported as 99% pure but shows visible shoulders may be masking co-eluting impurities.
- Retention time — the time at which the main peak elutes should be consistent with the expected hydrophobicity of the reported peptide sequence.
For a deeper explanation of what HPLC measures and how reverse-phase separation works for peptides, see the related article on HPLC testing for research peptides.
Interpreting Mass Spectrometry Data
Mass spectrometry (MS) data confirms molecular identity — it tells you whether the compound in the vial is actually the peptide the supplier claims it is. HPLC measures purity but cannot distinguish between two compounds of similar polarity that co-elute; MS provides the molecular weight fingerprint that resolves identity questions HPLC cannot.
On a peptide COA, MS results are typically reported as observed m/z values alongside the expected theoretical m/z for the target peptide. Peptides are analyzed as multiply charged ions, so you will often see several m/z values corresponding to different charge states (e.g., [M+2H]2+, [M+3H]3+, [M+4H]4+). Each of these should back-calculate to the same neutral mass, which should match the theoretical monoisotopic or average mass of the peptide.
If the MS data shows a mass offset from the expected value — even a small one — investigate before use. Common explanations include oxidized methionine residues (adds ~16 Da), missed deprotection during synthesis, or incorrect sequence assembly. For modified peptides such as Tesamorelin or CJC-1295 with DAC, the expected mass includes the modification — verify that the modification is accounted for in the theoretical value on the COA.
Peptide Content vs. Gross Weight
One of the most commonly overlooked fields on a peptide COA is peptide content — sometimes called net peptide content or corrected peptide content. This figure accounts for the fact that lyophilized peptide vials contain more than just the peptide. Water (moisture) and counter-ions (typically trifluoroacetate or acetate salt from the purification process) contribute to the total measured mass without contributing peptide.
A vial labelled as "10 mg" may contain only 7–8 mg of actual peptide if the water content is 10–15% and the TFA salt content is significant. Peptide content is typically determined by amino acid analysis (AAA) or calculated from water content measured by Karl Fischer titration.
When comparing supplier pricing, peptide content data allows accurate comparison: a supplier charging less per vial but providing 65% net peptide content may be offering less actual compound than a higher-priced supplier with 85% peptide content. If a COA does not report peptide content or water content, the nominal vial weight is not a reliable guide to the amount of compound you are receiving.
Red Flags on Supplier COAs
Experienced researchers learn to recognize COA documents that do not reflect genuine third-party analysis. Common red flags include:
- No chromatogram image — a purity percentage without a supporting chromatogram cannot be independently evaluated. Legitimate HPLC results include the raw chromatogram.
- No lot number — a COA without a lot number cannot be matched to a specific batch, making it effectively a generic document.
- No testing laboratory identified — the COA should name the laboratory that performed the analysis. In-house testing is not automatically invalid, but third-party testing by an independent laboratory carries more weight.
- Implausibly round purity numbers — a result reported as exactly 99.00% or 98.00% without decimal variability may suggest the document was not generated from actual analytical data.
- MS data absent for modified peptides — compounds with N-terminal or C-terminal modifications, PEGylation, or conjugated fatty acids require MS confirmation to verify the modification is present. A COA reporting only HPLC purity for such compounds is incomplete.
- Testing date significantly predates your order — peptides can degrade over time. A COA from several years before your purchase does not reflect current batch quality.
Why Third-Party Testing Matters
Third-party testing means that the analytical work was performed by a laboratory that is independent from the manufacturer. The significance of this independence is straightforward: a supplier testing their own products has a financial incentive to report favourable results. An independent laboratory has no stake in the outcome and applies standard analytical methodology without that conflict.
Reputable research peptide suppliers submit samples to accredited third-party analytical laboratories — often ISO 17025-accredited — and make the resulting COAs available to customers. The laboratory name, accreditation status, and contact information on the COA allow researchers to verify the testing entity if needed.
In practice, third-party testing adds cost that is reflected in pricing. Suppliers offering research peptides at prices significantly below market norms are often cutting corners on analytical documentation. This does not guarantee low quality, but it warrants additional scrutiny of whatever documentation is provided.
Applying COA Data to Your Research Workflow
Once you have evaluated a COA and confirmed that purity, identity, and peptide content meet your research standards, the COA data informs several practical decisions in your laboratory workflow. Peptide content figures allow accurate calculation of stock solution concentrations. HPLC purity data can be incorporated into methods sections of research documentation to characterize the compound used.
If your institution requires documentation of source compound quality for internal review, ethics approval, or grant reporting purposes, the COA is the primary document for that purpose. Retain the COA alongside your batch records for the full duration of the research project.
For questions about COA access and documentation for specific products, visit the lab testing page or reach out through the contact form. The FAQ also addresses common questions about COA interpretation and documentation standards. To view available research compounds, browse the full catalog.