Peptide

A peptide is a short chain of 2-50 amino acids linked by chemical bonds, serving as a fundamental biological building block. Peptides are distinct from proteins, which consist of longer folded chains of 51 or more amino acids, and from free amino acids, which are single units that are not linked together.

Standard peptide lab-test measurements

• HPLC (High-Performance Liquid Chromatography): This method measures peptide purity by determining the percentage of the sample that consists of the target compound compared to impurities.
• MS (Mass Spectrometry): This test verifies peptide identity by checking if the molecule's mass matches the expected chemical sequence.

Purity and identity are separate checks

Purity and identity are separate measurements that answer different questions about a peptide sample. A purity percentage indicates how much of the sample consists of one compound, but it does not confirm that the compound is the correct peptide. A sample could be 99% pure and still be the wrong molecule entirely.

A matching molecular weight confirms that the expected formula is present but does not measure how much of the batch is contaminated with byproducts. A common error is treating purity as identity, as a 98% pure value measures relative abundance rather than molecular correctness. Some Certificates of Analysis (COAs) lack sequencing or independent testing evidence, which is necessary to confirm safety and correctness.

Sources

1. Biochemistry, Peptide - StatPearls - NCBI Bookshelf
2. Systematic Errors in Peptide and Protein Identification and Quantification by Modified Peptides *
3. Liquid Chromatography-High Resolution Mass Spectrometry for Peptide Drug Quality Control - PMC
4. Peptide Mapping for Sequence Confirmation of Therapeutic Proteins and Recombinant Vaccine Antigens by High-Resolution Mass Spectrometry: Software Limitations, Pitfalls, and Lessons Learned - PMC
5. Explainer: Peptides vs proteins - what's the difference? - Institute for Molecular Bioscience - University of Queensland
6. HPLC and Mass Spectrometry for Peptide Validation
7. Peptide Testing: HPLC & Mass Spec Purity Guide | Apex
8. Peptide Certificates of Analysis: How to Read and Verify a COA ...
9. The difference between peptides and proteins
10. How to Test Peptides for Purity: HPLC, MS & COA Guide
11. IUPAC - peptides (P04479)
12. Reference Standards to Support Quality of Synthetic Peptide Therapeutics
13. How to Read a Peptide Certificate of Analysis (CoA) | Peptra Labs
14. HPLC vs Mass Spectrometry for Peptide Purity Testing - CertaPeptides
15. Certificates of Analysis: What Researchers Need to Know
16. Peptide
17. Peptide Testing Lab | HPLC Purity & Identity COA - Prodigy Labs
18. Proteins - Peptides - Amino acids: What are the differences