A Certificate of Analysis is your single most important quality verification document when sourcing research-grade peptides. Understanding how to interpret HPLC results, purity percentages, and testing methodology separates informed practitioners from those relying on blind trust.
What Is HPLC and Why Does It Matter?
High-Performance Liquid Chromatography (HPLC) is the gold standard for peptide purity analysis. This analytical technique separates the components of a peptide sample and quantifies the relative abundance of each. The result is a chromatogram, a graph showing peaks that correspond to different molecular species in the sample.
The main peak represents your target peptide, while smaller peaks indicate impurities such as deletion sequences, truncated peptides, or oxidation products. A purity of 98% or higher, as measured by HPLC, is generally considered research-grade quality for most therapeutic peptides.
Understanding Purity Percentages
When a COA states a purity of 99.2%, this means that 99.2% of the detected material in the HPLC analysis corresponds to the target peptide. The remaining 0.8% consists of related peptide impurities. It is important to note that HPLC purity does not account for non-peptide contaminants such as residual solvents, salts, or endotoxins, which require separate testing.
Be wary of suppliers who report purity without specifying the analytical method. "Purity: 99%" without mention of HPLC, the column type, mobile phase conditions, or detection wavelength is essentially meaningless. A complete COA should specify all analytical parameters used.
Mass Spectrometry Confirmation
While HPLC tells you how pure your sample is, mass spectrometry (MS) confirms that the peptide is actually the correct molecule. The observed molecular weight should match the theoretical molecular weight within acceptable tolerances. Electrospray ionization mass spectrometry (ESI-MS) is the most common method used for peptide identity confirmation.
A discrepancy between observed and expected molecular weight could indicate an incorrect sequence, chemical modifications, or degradation. Always check that the MS data on the COA confirms the identity of the peptide you ordered.
Endotoxin and Sterility Testing
For injectable peptides, endotoxin testing via the Limulus Amebocyte Lysate (LAL) assay is critical. Endotoxins are bacterial cell wall components that can cause severe inflammatory reactions. The USP limit for injectable products is typically less than 5 EU/kg of body weight. Your COA should report endotoxin levels well below this threshold.
Sterility testing, bioburden analysis, and residual solvent testing are additional quality parameters that a comprehensive COA may include, depending on the intended application of the peptide.
Red Flags on a COA
Watch for COAs that lack a batch or lot number, as this makes traceability impossible. Other red flags include the absence of a testing laboratory name, missing dates, results that seem templated across different products, and purity values that are suspiciously identical across multiple batches. A legitimate COA should be unique to each batch tested.
