Identity¶

Definition¶

Identity is the confirmation that a peptide sample is the correct molecule as specified, verified through analytical methods that confirm its molecular weight, sequence, and structural characteristics.

Overview¶

Identity testing answers the question: "Is this the right peptide?" While purity measures how clean the sample is, identity confirms what the sample actually is. Both are essential quality attributes.

Technical Explanation¶

Primary Identity Methods: - Mass Spectrometry (MS): Confirms experimental molecular weight matches theoretical value (most common) - Amino Acid Analysis (AAA): Confirms amino acid composition - Sequencing (MS/MS, Edman): Confirms actual amino acid order - Co-elution with Reference Standard: Retention time match on HPLC

Identity Verification Flow: 1. Calculate theoretical molecular weight from sequence 2. Acquire MS spectrum of the sample 3. Confirm observed molecular weight (m/z) matches theoretical 4. For modified peptides, confirm modification mass is included

Importance in Peptide Documentation¶

Identity data is a mandatory component of every Certificate of Analysis. Without identity confirmation, purity data alone is insufficient — a sample could be 99% pure but be the wrong peptide.

Frequently Asked Questions¶

Q: What is the most common identity test for peptides? A: Mass spectrometry (MS or LC-MS) is the most common and efficient method. It provides direct molecular weight confirmation.

Q: Can identity fail even if the purity is high? A: Yes. A sample could be 99% pure by HPLC but be a different peptide entirely (or contain the wrong modification). This is why identity testing is mandatory alongside purity testing.