Published by Hytanbio Tech · Technical guide · 31 October 2026
A single “purity” figure cannot answer every peptide quality question. A chromatogram, a content assay and a mass spectrum examine different attributes. Buyers who keep those results separate can compare batches without mistaking a clean chromatographic trace for a complete release package.
What each result actually supports
HPLC related-substance profile
High-performance liquid chromatography (HPLC) separates components under a specified column, mobile phase, gradient, detector and integration rule. An area-percent result describes the signal in that method. It can miss a species that does not respond similarly at the selected wavelength, and two components may co-elute. Ask whether the method was shown to separate the known impurities for the sequence at issue.
Assay or peptide content
Assay estimates the amount of target peptide against a suitable reference and stated calculation. It may use chromatography, amino-acid analysis, quantitative NMR or another justified method. The result should say whether it is reported on an as-is, dry or peptide-base basis. This matters when a lyophilized powder also contains water or counterions; see the salt-form specification guide.
Identity by LC-MS and other methods
Liquid chromatography–mass spectrometry (LC-MS) can support molecular-mass identity and reveal some sequence-related variants. A matching intact mass alone may not prove every residue position or stereochemical assignment. The EMA’s 2026 synthetic-peptide guideline recommends at least two orthogonal identification methods for synthetic medicinal peptides and warns about co-eluting impurities. That is a medicine-development standard, offered here as an analytical reference rather than a blanket cosmetic rule.
Read the COA beside the method
A batch COA is more useful when each number is traceable to a method and acceptance criterion. For a custom sequence, request:
- Sequence, terminal modifications and supplied form, including salt form where relevant.
- HPLC method identity, detection wavelength, integration convention and chromatogram for the offered lot.
- Identity method and observed result, including LC-MS information when available.
- Assay method and reporting basis; water and counterion tests if needed for the mass calculation.
- Defined known impurities, reporting limits and the treatment of unresolved peaks.
The EMA guideline explains why an additional method may be needed when one procedure cannot resolve all relevant peptide-related impurities. Its published reporting threshold for synthetic medicinal peptides is 0.1% in that regulatory context. It is not a universal release limit for every material on this website. Buyers should agree an application-specific specification rather than copy a number into an RFQ.
A practical comparison of two lots
First confirm that both lots have the same sequence, salt form and analytical method version. Then compare the main-peak area, the pattern of named and unknown peaks, the assay basis and any water or counterion results. If the method changed, ask for a bridge or a side-by-side test; a different gradient or detector can change the apparent area-percent profile without changing the material.
For scale-up, keep the original sample’s analytical record. It gives the team a concrete reference when discussing a later production lot. Our batch comparability guide covers the wider change-control discussion.
Frequently asked questions
Can LC-MS replace the HPLC purity result?
Usually not. The tests answer different questions. A method may combine chromatographic separation with mass detection, but the resulting identity and impurity assessments still need their own interpretation.
Why can two suppliers report different purity for the same sequence?
Different methods, integration rules, reference materials and salt forms can produce numbers that are not directly comparable. Ask for the method and chromatogram before drawing a conclusion.
Is a chromatogram enough to release a lot?
Only if the agreed specification says so, which is uncommon for a material with multiple relevant quality attributes. Identity, assay and other tests may be needed according to intended use.
References and scope
- EMA, Guideline on the Development and Manufacture of Synthetic Peptides.
- ICH Q6B, specifications for biotechnological/biological products, for the distinction among identity, purity, impurities and quantity in its stated scope.
- USP authors, Reference Standards to Support Quality of Synthetic Peptide Therapeutics.
Editorial scope: Analytical methods and acceptance criteria must be chosen for the material and end use. Request the batch-specific documents through our technical contact page.