CEI-MS-04 — Determination of water content in lyophilised peptides by coulometric Karl Fischer…
Determination of water content in lyophilised peptides by coulometric Karl Fischer titration
§1Scope
§1.1Scope
Applies to lyophilised peptide powders. Coulometric titration is specified rather than volumetric because sample availability is typically limited to a few milligrams.
§2Principle
Iodine generated coulometrically at an anode reacts stoichiometrically with water in the presence of sulfur dioxide and an alkylimidazole base. The charge required is proportional to the water present by Faraday’s law, with one mole of water consuming 2 × 96 485 coulombs. The method determines total water including both surface-adsorbed and lyophilisation-residual water.[1,2]
§3Apparatus and reagents
§3.1Apparatus
- Coulometric Karl Fischer titrator with a generator electrode, a double-platinum indicator electrode and a sealed titration cell
- Desiccated glove bag or dry-nitrogen-purged enclosure for sample transfer
- Analytical balance readable to 0.01 mg, inside or immediately adjacent to the dry enclosure
- Septum-sealed weighing vials
§3.2Reagents and reference materials
- Coulometric Karl Fischer reagent, anolyte and catholyte, appropriate to a peptide matrix
- Water standard, 1.00 mg/g, for system verification
- Dry nitrogen, ≤ 3 ppm water
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 ⟨921⟩ Water Determination. 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
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