A Review of Approaches for the SI Traceable Value Assignment of the Purity of Peptides Using the Model Compound Angiotensin I
Ralf D. Josephs, Norbert Stoppacher, Adeline Daireaux, Tiphaine Choteau, Katrice A. Lippa, Karen W. Phinney, Steven Westwood, Robert Wielgosz
Accurate diagnosis, monitoring and treatment are cornerstones of a healthcare system and require reliable and consistent measurements. The traceability of measurement results to stated references, and the development of Reference Measurement Systems (RMS), provide mechanisms to achieve the required consistency of results for laboratory medicine. The primary standards within such an RMS are certified reference materials of pure substances. Developments in modern measurement and mass spectrometric techniques have opened up the possibility to fully characterize and quantify more complex large molecules such as peptides, enabling RMS to be developed for these analytes. The renin-angiotensin system plays an important role in regulating blood volume, arterial pressure, and cardiac and vascular function. Management of this pathway has become very important in the treatment of high blood pressure and heart failure. The prohormone angiotensin I (ANG I) [amino acid sequence: DRVYIHPFHL] is a hypertension biomarker and was selected as a model peptide. The full mass balance approach, the peptide impurity corrected amino acid analysis (PICAA) approach, the peptide impurity corrected elemental analysis (PICCHN) approach and the quantitative nuclear magnetic resonance corrected for impurities (PICqNMR) approach have been investigated and optimized to compare and review the performance of these different methodologies for the purity mass fraction value assignment of an ANG I calibrator material. Excellent agreement of ANG I purity mass fraction values was obtained using this ensemble of approaches.