Peptide Purity Analysis

Reverse-phase C18 gradient with TFA or formic acid modifier is the default. For very hydrophilic or charged peptides, HILIC may resolve better.

Include method parameters, system suitability, the chromatogram itself, the integration table, and the calculated purity percentage. Sign and date the report.

Purity analysis in the strict sense is the HPLC main-peak measurement. But a batch that is fit for a protocol has usually passed a wider panel: identity by mass spectrometry, water content by Karl Fischer titration, residual solvent screening, acetate or counter-ion content for salt forms, and — for cell-culture work — endotoxin testing. Each panel answers a question the others can't: HPLC says how much of the sample is the main component; MS says what that component is; water and counter-ion analysis say what else the vial contains by mass.

When comparing suppliers, the width of this panel is a better quality signal than the purity number itself, because a 99% purity claim on a one-line certificate is unverifiable, while a 99% claim with the full panel behind it can be audited field by field.

Analytical competence exists in both settings; the difference is incentive structure. An in-house laboratory answers to the seller, and the number it reports can drift — not necessarily through dishonesty, but through method choice, integration conventions and the absence of any external counterparty to check against. An independent laboratory's report is produced for the transaction, not by it.

This is the reason third-party verification is treated as the reference standard in the research community, and why the certificates shipped with Bio Mech batches name the laboratory, the analyst and the date. A number you can trace to an independent instrument is a number you can build a protocol on.