Interpreting Certificates of Analysis

What is a Certificate of Analysis?

A Certificate of Analysis (COA) is an official document from a quality control laboratory that reports the results of analytical testing performed on a specific batch or lot of material. For research peptides, COAs typically include purity data (HPLC), identity confirmation (MS), appearance description, and lot-specific information. COAs serve as quality documentation that a product meets its specifications and provide traceability for research records. Reputable suppliers provide COAs for every lot they sell.

Key Information on a Peptide COA

Essential elements to review: (1) Product identification—peptide name, sequence, molecular formula, and theoretical molecular weight; (2) Lot/batch number—must match the product you received; (3) Purity—typically HPLC purity percentage, should meet stated specifications (e.g., ≥98%); (4) Molecular weight—observed MS value compared to theoretical, confirming identity; (5) Appearance—visual description (usually white to off-white powder); (6) Testing date—should be recent relative to product age; (7) Specifications—acceptance criteria for each test; (8) Analyst signature or authorization.

Understanding Purity Specifications

Purity on COAs is typically reported as 'HPLC purity' or 'Net peptide content.' These differ: HPLC purity reflects chromatographic separation of peptide-related components, while net peptide content accounts for water, counter-ions (TFA, acetate), and residual solvents—often 60-80% for lyophilized peptides. A peptide can be >99% pure by HPLC but only 70% net peptide content. For calculating molar concentrations, use the net peptide content value if provided; for comparative purity assessment, use HPLC purity.

Mass Spectrometry Data on COAs

MS data confirms peptide identity. The COA should show: (1) Observed molecular weight—from ESI-MS or MALDI-TOF; (2) Theoretical molecular weight—calculated from sequence; (3) Mass difference—should be within acceptable tolerance (typically <0.5 Da for peptides <3000 Da, or <0.1% for larger peptides). Some COAs show the actual MS spectrum or deconvoluted mass spectrum. If observed and theoretical masses don't match, the product may be incorrect, degraded, or have unexpected modifications.

Third-Party vs. In-House COAs

COAs can be generated by the manufacturer's in-house QC lab or by independent third-party laboratories. Third-party COAs provide additional assurance since the testing lab has no financial interest in the results. For critical research, consider: (1) Requesting third-party COAs if only in-house testing is provided; (2) Sending samples to your own analytical lab for verification; (3) Using multiple suppliers and comparing results. Reputable suppliers welcome questions about their testing procedures and may provide additional documentation upon request.

Limitations and Best Practices

Important limitations of COAs: (1) They represent testing at a specific point in time—storage conditions afterward affect actual quality; (2) They don't guarantee sterility, endotoxin levels, or bioactivity unless specifically tested; (3) They may not detect all possible impurities or degradation products; (4) Quality can vary between lots from the same supplier. Best practices: Always match lot numbers, verify specifications meet your requirements, store properly after receipt, consider periodic re-testing for critical applications, and maintain COAs as part of your research documentation.

Key Takeaways