Reading and Requesting a Certificate of Analysis (COA)

What is a Certificate of Analysis?

A Certificate of Analysis (COA) is a document issued by a testing laboratory that reports the results of analytical testing performed on a specific lot of a compound. For research peptides, a COA typically includes identity confirmation (confirming the compound is what it is labeled as) and purity assessment (quantifying the proportion of the target compound relative to impurities).

A COA is lot-specific — it applies to the specific batch of material tested, not to the product in general. When evaluating a supplier's quality claims, a COA from a laboratory independent of the supplier carries more weight than an in-house document, because it removes the conflict of interest inherent in self-testing.

HPLC purity: what the number means

High-Performance Liquid Chromatography (HPLC) is the standard analytical method for quantifying peptide purity. The sample is injected into a column and separated by its chemical properties; a detector (typically UV at 214–220nm, which measures peptide bonds) records the signal as the compound elutes. The area under the peak for the target compound, expressed as a percentage of the total peak area, is the reported purity.

A purity of ≥99% means that at least 99% of the UV-absorbing material in the sample is the target peptide. The remaining ≤1% may include synthesis-related impurities (truncated sequences, deletion peptides, oxidized variants) or residual reagents. Sealed Peptides lists a stated purity target of ≥99% across its catalog; the figure for your lot is on its COA.

When reading an HPLC chromatogram on a COA, look for: a single dominant peak (indicating high purity), the retention time of the main peak (which should match the expected value for the compound), and the area percentage. Multiple peaks of comparable size indicate a low-purity sample.

Mass spectrometry identity confirmation

Mass spectrometry (MS) confirms the molecular identity of the compound by measuring its molecular weight. The instrument ionizes 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 within the instrument's tolerance (typically ±0.1–0.5 Da for small peptides; ±1–2 Da for larger ones).

A COA that includes both HPLC purity and MS identity confirmation provides two independent lines of evidence: that the material is pure (HPLC) and that it is the correct compound (MS). HPLC alone cannot confirm identity — a highly pure sample of the wrong peptide would still show ≥99% purity by HPLC. MS alone cannot confirm purity — it detects the presence of the target compound but does not quantify impurities. Together, they provide a meaningful quality assurance package.

How to request a COA from Sealed Peptides

Sealed Peptides provides lot-level COA documentation on request. To request a COA for your order:

1. Use the Request lot COA button on any product detail page — this pre-populates the request with the product name.
2. Alternatively, email support@sealedpeptides.com with subject line "COA Request — [Product Name]" and include your order number.
3. Include the lot number from your vial label if available — this ensures you receive documentation matched to your specific batch.

COA availability varies by lot. Our team responds within one business day.