How to Verify a Peptide Certificate of Analysis

A certificate of analysis (COA) is the primary document researchers use to verify the quality of a peptide compound before it enters the laboratory. Understanding how to read one correctly, and what to look for, is an essential skill for anyone conducting serious peptide research in New Zealand.

This guide explains the structure of a standard peptide COA, what each section confirms, and how to identify documents that do not meet research standards.

What Is a Certificate of Analysis?

A COA is a quality assurance document issued by a laboratory that has tested a specific batch of a compound. It records the results of analytical tests performed on that batch and confirms whether the compound meets defined specifications for purity, identity, and quality.

For peptide compounds, a COA typically includes results from two core analytical methods: high-performance liquid chromatography (HPLC) and mass spectrometry (MS). Together, these two tests confirm both what the compound is and how pure it is.

All compounds at Eterna Peptides come with third-party COAs that you can review before purchase. Visit the COA page to access batch certificates.

The Key Sections of a Peptide COA

Product Identification

The header of a COA should clearly state:

• The compound name (both common name and, where applicable, systematic name or sequence)
• The batch or lot number
• The date of manufacture and date of analysis
• The mass or quantity tested
• The name of the testing laboratory

Cross-reference the batch number on the COA with the batch number printed on the vial you receive. If these do not match, contact your supplier before proceeding.

HPLC Purity Result

High-performance liquid chromatography separates the components of a sample and measures the relative proportion of each. For peptide purity testing, the result is expressed as a percentage representing the proportion of the target compound relative to all detected peaks.

What to look for:

• Purity of 98% or above is the standard for research-grade peptides. Some compounds are available at 99%+ purity.
• Purity below 95% is not suitable for controlled laboratory research, as the impurity load introduces uncontrolled variables.
• The COA should include the HPLC chromatogram or at minimum state the analytical method used (e.g., reverse-phase HPLC with UV detection at 214 nm).

Mass Spectrometry (Identity Confirmation)

Mass spectrometry measures the molecular mass of the compound. For a peptide, this confirms that the amino acid sequence produces a molecule of the expected molecular weight. A correctly synthesised peptide will have a specific, predictable molecular weight derived from the sum of its constituent amino acids.

What to look for:

• The observed molecular weight (m/z value) should match the theoretical molecular weight for the stated peptide.
• A tolerance of plus or minus 0.5 Da is acceptable for most peptide MS results.
• MS does not measure purity directly. It confirms identity only. Both HPLC and MS results are required together to fully characterise a compound.

Water Content (Karl Fischer Titration)

Lyophilised peptides retain some residual water content after the drying process. The water content affects the true peptide mass per unit weight. A COA may report water content as a percentage, which allows researchers to calculate the effective peptide content of a given vial mass.

For example, a vial stated to contain 10mg of peptide with 5 percent water content contains approximately 9.5mg of actual peptide. This is relevant when preparing solutions of known concentration for assay use.

Residual Solvents

Peptide synthesis uses organic solvents that must be removed from the final product. A thorough COA will include testing for residual solvents such as acetonitrile, DMF, or TFA, confirming these are below acceptable limits.

Red Flags in Peptide COA Documents

Not all COAs meet the standard required for reliable research. Watch for these warning signs:

• No laboratory name or accreditation number: An anonymous or unidentifiable testing laboratory is not credible.
• Purity stated without method: A purity percentage without specifying the analytical method (HPLC, UV wavelength, column type) is unverifiable.
• Missing MS data: A COA showing only HPLC results without mass spectrometry confirmation cannot verify compound identity.
• Generic or undated documents: COAs without batch numbers or analysis dates may be fabricated or reused across batches.
• In-house testing only: Supplier-issued COAs without third-party confirmation represent a conflict of interest.

Verifying COA Authenticity

For added confidence, some researchers contact the testing laboratory directly to confirm the document is genuine and relates to the batch in question. Reputable laboratories maintain records and can confirm document authenticity upon request.

Third-party testing laboratories commonly used in the peptide research supply chain include those operating under ISO/IEC 17025 accreditation, which is the international standard for testing laboratory competence.

Applying COA Information to Your Research

Once you have confirmed a COA is legitimate and the compound meets purity specifications, record the following in your laboratory documentation:

• Supplier name and order reference
• Compound name, batch number, and reported purity
• Date of receipt and storage conditions applied
• Link or file reference to the COA document

This documentation supports research integrity and allows you to reference the exact batch of compound used when writing up experimental results.

For New Zealand researchers sourcing peptides from Eterna Peptides, all batch COAs are available for download via the COA verification page before and after purchase.

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