Peptide Purity

Why purity matters and how HPLC analysis ensures research-grade quality.

FOR RESEARCH USE ONLY. This material is sold for laboratory research purposes only. Not for human consumption, veterinary use, or any diagnostic/therapeutic applications.

Peptide Purity: Measurement, Standards, and Significance

Purity is the single most important quality metric for research peptides. It directly affects experimental reproducibility, data reliability, and the validity of research conclusions. A peptide reported at 99% purity contains at least 99% of the target compound by weight, with the remaining fraction consisting of closely related impurities, salts, or residual solvents.

How Purity Is Measured

High-Performance Liquid Chromatography (HPLC) is the gold standard for peptide purity determination. In a typical HPLC purity analysis:

  1. A small sample of the peptide is dissolved in an appropriate solvent
  2. The solution is injected onto a reversed-phase C18 column
  3. A gradient of increasing organic solvent (typically acetonitrile) elutes compounds based on hydrophobicity
  4. A UV detector at 214 nm records the absorbance of the eluent over time, producing a chromatogram
  5. Purity is calculated as the area under the target peak divided by the total area of all peaks, expressed as a percentage

Purity Grades

Research peptides are typically available in several purity grades:

  • Crude (50-75%): Unprocessed synthesis output, suitable for preliminary screening only
  • Desalted (>75%): Salt-removed but not chromatographically purified
  • >95%: Standard research grade, acceptable for most cell-based and biochemical assays
  • >98%: High purity, suitable for in vivo studies and quantitative assays
  • >99%: Ultra-high purity, required for pharmacological studies and receptor binding assays where trace impurities could confound results

Epiq Aminos supplies all peptides at a minimum purity of 99% as verified by HPLC, ensuring researchers receive materials suitable for the most demanding experimental protocols.

Common Impurities

Impurities found in peptide preparations typically fall into several categories:

  • Deletion sequences: Peptides missing one or more amino acid residues due to incomplete coupling during synthesis
  • Truncated sequences: Shorter fragments resulting from premature chain termination
  • Oxidized species: Methionine and cysteine residues are particularly susceptible to oxidation
  • Diastereomers: Peptides containing one or more D-amino acids instead of the intended L-configuration
  • TFA/acetate salts: Counter-ions from the purification process

Why Purity Matters

Using peptides of insufficient purity can lead to irreproducible results, false positives in binding assays, unexpected cytotoxicity in cell culture, and erroneous dose-response relationships. In competitive binding studies, even 1-2% of a closely related impurity can significantly shift IC50 values. For any quantitative research application, peptide purity should be verified before use.

Certificate of Analysis

Every lot of peptide sold by Epiq Aminos includes a Certificate of Analysis (COA) documenting HPLC purity, mass spectrometry identity confirmation, and appearance. Researchers should review the COA for every lot received and retain it for their records.

Related Topics

For research use only. Not for human consumption. All products sold by Epiq Aminos are intended for laboratory research purposes only.