Leveling Effect: Very weak basic drugs (e.g., diazepam, chlorpheniramine, ciprofloxacin) cannot be reliably titrated in water because water behaves as a stronger base than the analyte, causing poorly defined endpoints.
Glacial Acetic Acid as Solvent: Glacial acetic acid acts as a protogenic/leveling amphiprotic solvent. It forces weak basic analytes (B) to accept protons:
The titration reaction proceeds with sharp potentiometric or visual (crystal violet / quinaldine red) inflection:
