How to Read a Certificate of Analysis

Why COAs Matter

A Certificate of Analysis (COA) is the single most important document for verifying the identity and purity of a research peptide. It provides analytical data from laboratory testing that confirms what is in the vial matches what is on the label. For any researcher working with peptide compounds, understanding how to read and evaluate a COA is a fundamental skill.

The Two Core Tests

HPLC Purity Analysis

High-Performance Liquid Chromatography (HPLC) is the gold standard for quantifying peptide purity. The technique works by separating compounds in a mixture based on their interactions with a stationary phase (typically a C18 reversed-phase column) as they are carried through by a mobile phase (solvent gradient).

On a COA, you will see:

• Purity percentage: Expressed as a percentage of the total peak area. Research-grade peptides typically show ≥98% or ≥99% purity.
• Retention time: The time (in minutes) at which the target peptide elutes from the column. This should match the expected value for that specific peptide.
• Chromatogram: A graph showing detector response over time. A clean COA shows one dominant peak (your peptide) with minimal secondary peaks (impurities).

When evaluating HPLC data, look for a single sharp, well-resolved main peak. Broad peaks, multiple peaks of similar height, or significant baseline noise can indicate degradation, aggregation, or impurities.

Mass Spectrometry (MS) Identity Confirmation

While HPLC tells you how pure the sample is, mass spectrometry tells you what it is. MS measures the mass-to-charge ratio (m/z) of ionized molecules, providing a molecular weight determination that serves as identity confirmation.

On a COA, you will see:

• Observed mass: The molecular weight measured by the instrument.
• Expected mass: The theoretical molecular weight of the target peptide.
• Mass spectrum: A graph showing signal intensity versus m/z values.

The observed mass should match the expected mass within the instrument tolerance (typically ±1 Da for ESI-MS, ±2-3 Da for MALDI-TOF). A significant discrepancy suggests the sample may be a different compound, a truncated sequence, or may contain modifications.

Third-Party vs. In-House Testing

This distinction is critical for research reliability:

• Third-party testing means an independent laboratory — one with no financial relationship to the vendor — performed the analysis. The lab has no incentive to produce favorable results. ISO/IEC 17025 accreditation adds an additional layer of quality assurance.
• In-house testing means the vendor tested their own product. While not inherently unreliable, it lacks the objectivity of independent verification.

Look for the laboratory name, any accreditation numbers, and a unique test identifier or batch number on the COA. A credible third-party lab will have its own branding, contact information, and test reference numbers that can be independently verified.

Batch-Specific vs. Generic COAs

A batch-specific COA corresponds to the exact lot of material you receive. It will have a batch or lot number that matches the label on your vial. This is the gold standard — it tells you about the specific material in your hands.

A generic COA may represent testing done on a different batch or at a different time. While it can indicate general product quality, it does not guarantee that your specific vial meets the stated specifications.

Red Flags to Watch For

• No laboratory name or accreditation information
• Missing chromatogram or mass spectrum images (data without graphs)
• Purity stated as a range (“95-99%”) rather than a specific measured value
• No batch or lot number linking the COA to specific material
• COA date significantly older than the product manufacture or purchase date
• Observed molecular weight that does not match the expected value

What a Good COA Looks Like

A reliable COA should include:

1. Laboratory name and accreditation details
2. Unique test/sample identifier
3. Compound name and CAS number
4. Batch or lot number
5. Test date
6. HPLC purity result with chromatogram
7. MS identity confirmation with spectrum
8. Analyst signature or electronic verification

Taking the time to evaluate COAs is a fundamental part of responsible research practice. The few minutes spent reviewing analytical documentation can prevent weeks of compromised experimental results.

All compounds discussed in this article are intended for in vitro research use only. Not for human or veterinary use.