Determination of thermodynamic dissociation constants of local anaesthetic amines: influence of ionic strength

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Abstract
Theoretical calculations, based on the Debye-Hückel theory, indicate that for weak monoprotic bases that do not involve a hydroxyl group (B) a stoichiometric pKa determined at any ionic strength compatible with an accurate determination (μ <0·10) should be no different from the thermodynamic pKa. The pKa's of two local anaesthetic amines were determined at several ionic concentrations. The resultant independence of the acidic dissociation constants on ionic concentration supports the theoretical considerations. The implications of these results in local anaesthetic research are discussed.