A Certificate of Analysis is the single most important quality document in peptide research. It tells you whether the compound in the vial is what the label claims, at the purity stated, and free from contaminants that could confound your results. Yet many researchers glance at the purity number and skip the rest. Here's how to read the full document and what each test actually measures.
HPLC Purity: The Headline Number
High-Performance Liquid Chromatography (HPLC) is the standard method for determining peptide purity. The sample is dissolved, injected into a chromatography column, and separated by hydrophobicity. A UV detector (typically at 220nm) measures the eluted peaks. The target peptide peak area, divided by total peak area, gives the purity percentage.
What to look for: The purity percentage (e.g., 98.7%), the retention time of the main peak, and the chromatogram itself showing a clean, sharp main peak with minimal secondary peaks. Impurities typically include deletion sequences (peptides missing one or more amino acids from the synthesis), truncated sequences, and oxidized variants.
Red flags: A purity claim without an accompanying chromatogram image. Unusually broad or shouldered main peaks (suggesting co-eluting impurities). Absence of method details (column type, mobile phase, gradient).
Mass Spectrometry: Identity Confirmation
While HPLC tells you how pure the sample is, mass spectrometry (MS) tells you whether it's the right compound. The peptide is ionized and its mass-to-charge ratio is measured. The observed molecular weight must match the theoretical molecular weight within instrument tolerance (typically ±0.1%).
What to look for: The observed mass matching the expected molecular weight. For BPC-157, you'd expect approximately 1419.5 Da. For TB-500, approximately 4921.5 Da. Common MS techniques include ESI-MS (electrospray ionization) and MALDI-TOF.
Red flags: An observed mass that doesn't match the expected value, multiple dominant mass peaks suggesting a mixture, or absence of MS data entirely.
Amino Acid Analysis
Amino acid analysis (AAA) hydrolyzes the peptide and quantifies each constituent amino acid. The observed amino acid ratios should match the theoretical composition. This test complements MS by confirming not just molecular weight but actual composition.
Endotoxin Testing (LAL)
Endotoxins are lipopolysaccharides from gram-negative bacteria that can cause inflammatory responses in biological systems. The Limulus Amebocyte Lysate (LAL) test detects endotoxin contamination. For injectable research peptides, endotoxin levels should be below 0.5 EU/mg.
Appearance and Solubility
COAs typically note the peptide's physical appearance (e.g., "white lyophilized powder") and solubility characteristics. While seemingly basic, appearance verification catches gross manufacturing errors — a peptide that should be white but appears yellow or discolored may indicate degradation.
Batch Number and Expiration
Every COA should reference a specific batch/lot number that matches the vial label. This ensures traceability. Expiration dates reflect stability testing data — lyophilized peptides stored properly at -20°C typically remain stable for 2+ years.
Why Third-Party Testing Matters
A COA issued by the same company selling the peptide carries inherent bias. Third-party testing by an independent laboratory (such as Janoshik Analytical or Colmaric Analyticals) provides unbiased verification. Research Vials includes third-party testing documentation with every product — available at researchvials.com.
COA Quick Checklist
- HPLC purity ≥95% (preferably ≥98%) with chromatogram image
- Mass spectrometry confirming expected molecular weight (±0.1%)
- Batch/lot number matching vial label
- Test date within product shelf life
- Endotoxin testing results (for injectable-grade compounds)
- Third-party laboratory attribution (ideally independent)