High-Performance Liquid Chromatography (HPLC) purity analysis is the standard method for quantifying peptide purity in research settings. The percentage reported on a Certificate of Analysis represents a specific measurement with defined parameters.
What HPLC Measures
Reverse-phase HPLC separates peptide components by hydrophobicity. The purity percentage reflects the area under the target peptide peak relative to all detected peaks in the chromatogram. A 99.4% purity result means the target peptide accounts for 99.4% of the UV-absorbing material detected at a given wavelength (typically 214 nm or 220 nm).
What HPLC Does Not Measure
HPLC does not detect all impurities. UV-transparent contaminants (inorganic salts, certain counter-ions) may not appear in the chromatogram. This is why reputable suppliers pair HPLC with mass spectrometry for identity confirmation.
Mass Spectrometry as Complementary Analysis
MS identity confirmation verifies the molecular weight of the target peptide matches the theoretical value within acceptable mass accuracy. This confirms that what was synthesized is what was ordered, regardless of purity percentage.
Interpreting COA Data
A complete COA should report: HPLC purity, MS identity confirmation, appearance, and lot number. The purity target for research-grade peptides is generally 98%+, with premium suppliers targeting 99%+.
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