Peptide content (revision 4)
Old revision·08:38, 1 Oct 2024·StubSorterBot
| Peptide content | |
|---|---|
| Analytical method infobox · conventions |
Peptide content, sometimes called peptide net content, is the proportion of the mass of a preparation that is the peptide itself. Everything else in the vial — water taken up during and after lyophilisation, the counterion left by the purification step, residual solvent, and any excipient — is excluded from the numerator and included in the denominator.[1]
Content is the determination that makes a mass statement possible. A purchaser reconstituting a nominally 5 mg vial and calculating a concentration is implicitly assuming a content figure, and in the ordinary case the assumption made is 100%, which is never correct for a lyophilised peptide salt. Typical content for such material falls between roughly 70% and 90%, so the assumption is wrong by an amount that matters.[1]
What occupies the rest of the mass
[edit]For a lyophilised peptide purified by reverse-phase chromatography and freeze-dried from an aqueous acetonitrile mobile phase, four components account for essentially all of the non-peptide mass.
| Component | Typical share | Determined by |
|---|---|---|
| Water | 3–10% | Karl Fischer titration or Loss on drying |
| Counterion (usually trifluoroacetate) | 5–20% | Ion chromatography; inferred from the synthesis route only as a last resort |
| Residual solvent | below 1% | Headspace gas chromatography |
| Peptide-related impurities | 0.5–3% | The complement of Area percent purity |
The acetonitrile carried over from preparative purification is the residual solvent that dominates in practice; it is classified for toxicity and given a concentration limit under the harmonised residual-solvent guideline, and it is determined by headspace gas chromatography rather than inferred.[2]
References
- ^ a b United States Pharmacopeia, General Chapter <1503>, "Quality Attributes of Synthetic Peptide Drug Substances" (informational). USP–NF, current revision. Sets out peptide content as an attribute distinct from chromatographic purity.
- ^ International Council for Harmonisation, Q3C: Impurities — Guideline for Residual Solvents. Classifies solvents by toxicity and sets concentration limits; the acetonitrile used in preparative purification falls in the second class.