I had questions about what was left in the remainder of the ~1% that isn't peptide on test results. Got this from Gemini and thought it was interesting:
Process-Related Impurities
These are non-peptide materials that remain from the reagents and solvents used during the synthesis and purification steps.
• Residual Solvents and Reagents: The final step of peptide synthesis often involves cleavage from the solid support using strong acids like Trifluoroacetic Acid (TFA). Some of this acid remains, and the peptide is often isolated as a TFA salt. Other solvents or scavengers (reagents used to prevent unwanted side reactions) can also remain.
• Salts and Buffers: The purification step, typically High-Performance Liquid Chromatography (HPLC), uses various buffers and salts. Trace amounts of these can remain in the final lyophilized (freeze-dried) powder.
• Elemental Impurities: Trace amounts of heavy metals or other elements that may have been present in the raw materials or from the reaction vessel can be present.
• Contaminating Peptides: In some rare cases, if multiple peptides are synthesized in the same facility, cross-contamination with a small amount of a completely different peptide can occur.