---
title: "How to read a certificate of analysis (CoA) | Sable Peptides"
description: "How to read a research peptide CoA line by line: lot number, lab and task number, HPLC purity, mass spectrometry identity, measured content and what each figure does and does not show."
canonical: https://www.sablepeptides.co.uk/guides/how-to-read-a-coa
dateModified: 2026-10-14
publisher: Sable Peptides Limited (UK company 17488610)
note: Research use only. Not for human or veterinary use.
---

# How to read a certificate of analysis (CoA)

A certificate of analysis reports what a laboratory measured on a sample from one lot. Read it from the top: first check it is about your vial, then what was measured, then how.

## Step 1: is it your lot?

-   Find the lot or batch number on the CoA and compare it with the label on your vial. They must match exactly.
-   Check the compound name and the stated vial amount match what you ordered.

## Step 2: who tested it, and when?

-   The laboratory should be named, with a task, report or sample number.
-   The test date should be before, or close to, the lot release date.
-   An independent laboratory is stronger evidence than an in-house report, and a report the lab can confirm is stronger still. See how to verify a CoA.

## Step 3: purity (HPLC)

HPLC purity is the main peak's share of the total detected peak area, usually measured by UV absorbance at around 214–220 nm. A figure such as 99.1% means 99.1% of what the detector saw was the main compound. It does not say how much peptide is in the vial, and impurities that do not absorb at that wavelength are not counted.

Look for the chromatogram itself: one dominant peak with small, well-separated minor peaks.

## Step 4: identity (mass spectrometry)

Mass spectrometry (LC-MS, ESI or MALDI) confirms identity by matching the measured mass to the theoretical mass of the sequence. The CoA should state both values. A close match confirms the molecule; it does not measure purity.

## Step 5: content or quantity

Some reports state the measured amount in the vial (for example 10.4 mg for a 10 mg vial). This is different from purity. Lyophilised peptides also contain water and counter-ions such as TFA or acetate, so net peptide content is normally below the gross weight.

## Other lines you may see

-   Appearance: usually a white lyophilised powder.
-   Water content (Karl Fischer) and counter-ion content.
-   Endotoxin (LAL) or sterility results, which are not standard for research-grade vials.

## Red flags

-   No lot number, or a lot number that does not match your vial.
-   No named laboratory, no report number, or a lab that cannot confirm the report.
-   Figures with no method or no date.
-   The same certificate used for several different lots.

## Related

-   [HPLC and MS explained](/guides/hplc-and-mass-spectrometry-on-a-peptide-coa)
-   [Purity vs net peptide content](/guides/peptide-purity-vs-net-peptide-content)
-   [Glossary of CoA fields](/learn/coa-fields)
-   [How to read an HPLC chromatogram](/learn/how-to-read-an-hplc-chromatogram)
-   [How to verify a CoA](/learn/how-to-verify-a-coa)
-   [Sable CoA library](/coa/library)
-   [Method validation terms (ICH Q2)](/guides/analytical-method-validation-terms-on-a-coa)
-   [Endotoxin testing](/guides/endotoxin-testing-for-research-peptides)
-   [Impurity thresholds](/guides/related-substances-and-impurity-thresholds)
-   [Measurement uncertainty](/guides/measurement-uncertainty-in-peptide-purity-results)

Updated 2026-10-14. Research use only. Not for human or veterinary use. No administration amounts or health claims are made.