Peptide quantitation

Peptide quantitation is the analytical process used to determine the exact mass or concentration of a specific peptide in a sample. This measurement assigns an absolute value, such as milligrams per vial for freeze-dried powders or molar concentration for solutions, to the target peptide, distinguishing it from purity, identity, or safety testing.

Standard laboratory methods provide precise peptide quantitation

• HPLC with UV detection is the standard approach for mass-content assignment in peptide quantitation.
• LC-MS/MS with targeted fragment detection offers high specificity and sensitivity for precise peptide measurement.
• Amino acid analysis (AAA) breaks the peptide into its constituent amino acids to back-calculate the original peptide amount.
• Quantitative NMR (qNMR) counts molecules directly and does not require a peptide-specific reference standard.
• Colorimetric assays like BCA or Kjeldahl nitrogen-determination are not reliable substitutes because they are not peptide-specific.

Purity levels do not reflect actual peptide content

Peptide purity and peptide content describe fundamentally different properties of a substance. A report showing '99% pure' describes the relative share of the main peak among all detected species in the sample, but it does not show how many milligrams of peptide are physically present in the vial.

Water, salts, and residual solvents remain invisible to a purity trace, yet they reduce the actual peptide mass. Without validated quantitation, a label claim of '10 mg' should not be assumed to mean 10 mg of actual peptide. Regulatory bodies require validated methods that demonstrate accuracy, precision, selectivity, and reproducibility to ensure reliable results.

Sources

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