Understanding Your Certificate of Analysis

How to Read Your Certificate of Analysis (COA)

Every peptide shipped from NXPeptides includes a Certificate of Analysis. The COA is essentially the quality report card for your specific batch, providing analytical data that confirms the identity and purity of what you received. Understanding how to read this document helps you evaluate product quality, troubleshoot experimental issues, and maintain proper records for your research.

This guide walks through each section of a typical COA, explains what the numbers mean, and helps you understand what to look for when evaluating peptide quality.

What is a COA?

A Certificate of Analysis is a quality control document generated for each production lot of a peptide. It contains the results of analytical testing performed on that specific batch. Think of it as a fingerprint for your peptide: it tells you what was made, how pure it is, and confirms that the product matches its intended specifications.

COAs are standard practice across the peptide industry and in research chemical supply more broadly. They are an important part of good laboratory practice and may be required by institutional review processes.

Key Sections of Your COA

Product Information

At the top of the COA, you will find basic product details:

Product Name: The common or catalog name of the peptide
Catalog Number: Our internal reference number
Lot Number: The unique identifier for this production batch. If you ever need to reorder the same batch or report an issue, reference this number.
Sequence: The amino acid sequence of the peptide, usually in single-letter code
Molecular Weight: The calculated molecular weight based on the amino acid sequence
Quantity: The net peptide content (how much active peptide is in the vial, accounting for salt and moisture content)

HPLC Purity Data

High-Performance Liquid Chromatography (HPLC) is the primary method used to measure peptide purity. On your COA, you will typically see:

Purity (%): This is the headline number most researchers look at. It represents the percentage of the total material that is your target peptide. NXPeptides products typically have purities of 98% or higher.
HPLC Chromatogram: Some COAs include the actual chromatogram, a graphical trace showing peaks detected during the HPLC run. The main peak represents your peptide. Smaller peaks are impurities (incomplete sequences, side products, etc.).
Retention Time: The time at which your peptide eluted from the HPLC column. This is primarily useful for analytical comparison and is not something you generally need to interpret.
Method Details: Column type, mobile phase composition, gradient conditions, and detection wavelength (usually 214 nm or 220 nm UV).

For a deeper understanding of how HPLC works in peptide analysis, see our HPLC Purification Methods guide.

Mass Spectrometry Data

Mass spectrometry (MS) confirms the identity of your peptide by measuring its molecular mass. On the COA, you will see:

Observed Mass (or m/z): The mass detected by the instrument. For singly charged ions, this is close to the molecular weight plus 1 (for the added proton). For multiply charged ions, the observed m/z will be lower.
Expected Mass: The theoretical molecular weight calculated from the amino acid sequence.
Mass Spectrum: Some COAs include the actual spectrum, showing peaks at different m/z values. The dominant peak should correspond to your peptide.

A close match between observed and expected mass (typically within 0.1% or within 1 Dalton for smaller peptides) confirms that the correct peptide was synthesized. Learn more in our Mass Spectrometry for Peptides guide.

Appearance

This section describes the physical form of the peptide, usually something like “white to off-white lyophilized powder.” Slight variations in appearance (slightly yellowish tint, slightly fluffy vs. compact powder) are normal and do not affect quality.

Solubility (if included)

Some COAs note recommended solvents and expected solubility. If yours does not include this, check our Solvent Selection Guide for recommendations.

Net Peptide Content

This is important and often misunderstood. The weight on the vial label (e.g., 5 mg) may refer to the gross weight, which includes the peptide plus counter-ions (like TFA or acetate salts) and residual moisture. The net peptide content tells you the actual amount of active peptide. It is typically 60% to 85% of the gross weight, depending on the sequence and salt form.

For precise concentration calculations, use the net peptide content rather than the gross weight.

What Purity Level Do You Need?

Different research applications have different purity requirements:

Greater than 98%: Suitable for quantitative assays, binding studies, structural biology, and any application where impurities could affect results
95% to 98%: Appropriate for most general research, screening assays, and antibody production
90% to 95%: May be acceptable for preliminary screening or when cost is a major factor
Below 90%: Generally not recommended for most research applications

NXPeptides standard catalog products are manufactured to 98% purity or higher. If you need a specific purity level for a custom synthesis project, let us know when you submit your request.

Red Flags to Watch For

While most COAs you receive from reputable suppliers will look fine, here are things that might indicate a problem:

Mass discrepancy of more than 1 to 2 Daltons from the expected value
Multiple large peaks in the HPLC chromatogram (low purity)
Missing or incomplete data sections
No lot number or inconsistent product information
Purity significantly lower than what was advertised

If something looks off on your COA, do not hesitate to reach out to us at support@nxpeptides.com. Our quality team can review the data with you and address any concerns.

Requesting a COA

A COA is included with every order from NXPeptides. If you need an additional copy or a COA for a previous order, simply email us at support@nxpeptides.com with the lot number or order number and we will send it over promptly.

Related Resources

All NXPeptides products are intended for research use only. Not for human consumption.