How to Read a Certificate of Analysis (COA): A Guide for Researchers

July 18, 2026

How to read a certificate of analysis COA guide by Alpha Peptides — HPLC purity data, mass spectrometry, batch traceability and quality control for research peptides.

Introduction

A Certificate of Analysis (COA) is one of the most important documents you will receive when purchasing research-grade peptides. It provides batch-specific analytical data confirming the identity, purity, and quality of the compound you have received. Understanding how to read and interpret a COA is an essential skill for any researcher working with peptide reagents.

This guide walks through the key sections of a typical peptide COA, explains what each data point means, and highlights what to look for when evaluating the quality of a research peptide.

What Is a Certificate of Analysis?

A COA is a quality control document issued by the manufacturer or supplier of a research compound. It summarises the results of analytical testing performed on a specific batch of the product, confirming that it meets defined quality specifications. For research peptides, a COA typically includes:

Product name and sequence
Batch or lot number
Molecular formula and molecular weight
Purity data (typically from HPLC analysis)
Identity confirmation (typically from mass spectrometry)
Physical appearance
Storage recommendations

Alpha Peptides provides a batch-specific COA with every product. You can access your product COA via the product page or by contacting us with your batch number.

Key Sections of a Peptide COA

1. Product Identification

The top section of the COA identifies the product. Check that the following match what you ordered:

Product name: The common name of the peptide (e.g., Semax, Epitalon, Tesamorelin)
Sequence: The amino acid sequence in single-letter or three-letter code (e.g., Met-Glu-His-Phe-Pro-Gly-Pro for Semax)
Molecular formula: The chemical formula of the peptide (e.g., C₃₇H₅₁N₉O₁₀S for Semax)
Molecular weight: The theoretical molecular weight in Daltons (Da) or g/mol
Batch/Lot number: A unique identifier for the specific production batch — important for traceability

2. Purity — HPLC Analysis

Purity is the most critical quality metric for a research peptide. It is determined by High-Performance Liquid Chromatography (HPLC), a technique that separates the components of a sample and quantifies them based on their retention time and UV absorbance.

The COA will report purity as a percentage, typically measured at 214 nm or 220 nm UV wavelength (which detects peptide bonds). For example: Purity: 98.7%

What does this mean? A purity of 98.7% indicates that 98.7% of the material in the vial is the target peptide, with the remaining 1.3% comprising impurities such as truncated sequences, deletion peptides, or residual synthesis reagents.

What purity should you look for?

≥98% purity — research grade; suitable for most in vitro laboratory research applications
≥95% purity — acceptable for some research applications but may introduce more variability
Below 95% — generally not suitable for precision research; impurities may confound results

All Alpha Peptides products are supplied at ≥98% purity by HPLC.

3. Identity — Mass Spectrometry (MS)

Mass spectrometry confirms the identity of the peptide by measuring its molecular mass. The COA will typically report:

Theoretical MW: The expected molecular weight calculated from the amino acid sequence
Observed MW (MS result): The molecular weight measured by the mass spectrometer

These two values should match closely (within instrument tolerance, typically ±0.1–0.5 Da). A match confirms that the compound in the vial has the correct molecular identity.

Example:

Theoretical MW: 857.96 Da
Observed MW: 857.9 Da ✓

If the observed MW does not match the theoretical MW, this is a significant quality concern and the product should not be used in research.

4. Appearance

The COA will describe the expected physical appearance of the product, typically something like: "White to off-white lyophilised powder".

Check your vial against this description upon receipt. Minor colour variation (e.g., slightly cream rather than pure white) is generally acceptable. Significant discolouration, clumping, or an unusual odour may indicate degradation and should be investigated before use.

5. Storage Conditions

The COA will specify recommended storage conditions for the lyophilised product, typically:

Short-term: −20°C
Long-term: −80°C
Protect from light and moisture

Always store peptides according to the COA recommendations. For full storage guidance, refer to our Peptide Storage & Handling Guide.

Red Flags to Watch For

When evaluating a COA from any supplier, watch for the following warning signs:

No batch number: A COA without a unique batch/lot number cannot be traced to a specific production run and may be a generic document not specific to your product.
Purity below 95%: Indicates significant impurities that may affect research outcomes.
Missing MS data: Without mass spectrometry confirmation, you cannot verify that the compound is what it claims to be.
MW mismatch: A discrepancy between theoretical and observed molecular weight is a serious quality concern.
No HPLC chromatogram: Reputable suppliers will provide the actual HPLC trace, not just a purity number. The chromatogram allows you to see the peak profile and assess impurity distribution.
Generic or undated COA: A COA should be specific to your batch and include a date of analysis.

Requesting Your COA

Every Alpha Peptides product is supplied with a batch-specific COA. You can access your COA:

Via the product page on our website (COA download link)
By contacting us with your order number and batch number

If you have questions about interpreting your COA or have concerns about a specific batch, please contact us and our team will be happy to assist.

Related Research Guides

Disclaimer: All products sold by Alpha Peptides are intended strictly for in vitro research and laboratory use only. They are not approved for human or veterinary use, and this article does not constitute medical advice.