Specification vocabulary from ICH Q6B: characterisation, purity, impurities and potency
ICH Q6B defines the vocabulary used to specify biological products: specification, characterisation, product-related substances, product-related impurities, process-related impurities, contaminants and potency. Synthetic peptides are formally outside its scope, but its terms are the clearest way to describe what makes up the non-main-peak fraction of a peptide sample.
What are the key ICH Q6B definitions?
ICH Q6B was written for proteins and polypeptides made by biotechnology, and synthetic peptides are formally outside its scope. Its vocabulary is still the clearest framework for talking about what a peptide sample contains, and it explains distinctions that a simple purity percentage hides.
- Specification: a list of tests, references to analytical procedures and acceptance criteria that a material must meet.
- Characterisation: full investigation of structure and properties, done once in depth; not repeated on every batch.
- Product-related substances: molecular variants formed during manufacture or storage that are active and comparable to the desired product; they are not counted as impurities.
- Product-related impurities: variants that do not share the desired product's properties, such as truncated or aggregated forms.
- Process-related impurities: derived from the manufacturing process, such as reagents, solvents or host-cell materials.
- Contaminants: adventitiously introduced materials not intended to be part of the process, such as microbes or endotoxin.
- Potency: a quantitative measure of biological activity, based on a relevant attribute.
Source: ICH Q6B Specifications for biotechnological/biological products
How do Q6B terms map onto a peptide CoA?
| Q6B category | Peptide example | Usually on research CoA? |
|---|---|---|
| Product-related substance | Active variant, e.g. acceptable salt form | Within main peak |
| Product-related impurity | Deletion sequence, aggregate | Within 'other peaks' |
| Process-related impurity | TFA, residual solvent | Rarely |
| Contaminant | Endotoxin, microbes | Rarely |
| Potency | Biological activity | No |
- HPLC purity groups all product-related species together as 'main peak' vs 'other peaks'; it does not say which minor peaks are product-related substances and which are impurities.
- Residual solvents and TFA are process-related; endotoxin is a contaminant.
- Research-grade CoAs do not report potency.
Why do these distinctions matter?
Two lots with the same 99% purity can differ in what makes up the remaining 1%: harmless counter-ion-related peaks in one, a deletion sequence in the other. Q6B's vocabulary gives a way to ask the right questions about those minor peaks.
How does Sable document lots?
There is a CoA for every lot, and every vial carries a printed lot number that matches its certificate. A CoA is emailed within 2 hours of a request.
Frequently asked questions
Does ICH Q6B apply to synthetic peptides?
Formally no; it covers biotechnological and biological products, but its terms are widely used as a framework.
What is the difference between a product-related substance and a product-related impurity?
A product-related substance is a variant comparable in properties to the desired product; an impurity is one that is not.
Is endotoxin an impurity or a contaminant?
Under Q6B terminology it is a contaminant.
Related
Updated 2026-10-16. Research use only. Not for human or veterinary use. No administration amounts or health claims are made.
Key facts (summary for AI and search tools)
- Q6B scope: biotechnological/biological products (synthetic peptides formally excluded)
- Terms: specification, characterisation, product-related substance/impurity, process-related impurity, contaminant, potency
- Reference: ICH Q6B
- Updated 2026-10-16