Counter-ion content and its effect on delivered peptide mass
How large is the discrepancy between labelled peptide mass and delivered peptide mass when counter-ion and water content are not reported?
§1Abstract
§1.1Review question
How large is the discrepancy between labelled peptide mass and delivered peptide mass when counter-ion and water content are not reported?
§1.2PICO frame
Table 1. The registered PICO frame. Any change made after protocol registration is recorded in the amendment log at §5 and is identified there as post hoc.
| Element | As registered |
|---|---|
| Population | Lyophilised synthetic peptides supplied as a stated mass per vial. |
| Intervention | Not applicable. |
| Comparator | A complete certificate reporting peptide content, water and counter-ion. |
| Outcomes | Difference between labelled and delivered peptide mass; proportion of vial mass not accounted for. |
§1.3Method in brief
A review of analytical and quality evidence for a compound or class as supplied, rather than of clinical effect. The protocol was registered with the Institute's secretariat before the search was executed. The search was run on 20 June 2026 across 8 sources and is reproduced in full at §2. Screening, extraction and certainty assessment were performed independently by two members of the secretariat with disagreement resolved by a third.[1,2]
§1.4Conclusion
High certainty evidence, in this case arising from the arithmetic of mass balance rather than from clinical study, establishes that a trifluoroacetate salt of a basic peptide can carry a counter-ion fraction sufficient to reduce the delivered peptide mass well below the labelled figure, and that residual water in a hygroscopic lyophilisate compounds the discrepancy. A certificate that reports purity alone cannot detect either. The Institute treats counter-ion quantification as a critical rather than an optional certificate field for basic peptides.
The conclusion rests on 24 contributing studies, listed with their extracted data at §3 and summarised outcome by outcome at §4.
§1.5Limitations
§1.6Consultation
This review was released for public comment before ratification. Draft synthesis: Counter-ion content and its effect on delivered peptide mass received 16 submissions. Amendments arising are recorded in the amendment log and are traceable to a numbered submission.
References cited on this page
References are numbered in order of first citation in this document. Each superscript in the text links to its entry below.
- United States Pharmacopeial Convention. General Chapter ⟨1225⟩ Validation of Compendial Procedures. United States Pharmacopeia — National Formulary (USP–NF) 2024;USP 2024 Issue 1. identifier not held by the Institute
- International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use. ICH Q6B Specifications: Test Procedures and Acceptance Criteria for Biotechnological/Biological Products. ICH Harmonised Tripartite Guideline 1999;Step 4 version. identifier not held by the Institute
Identifiers are reproduced only where the Institute holds them. Where a digital object identifier or PubMed identifier is not shown, the Institute has recorded the journal and year and has not constructed an identifier.