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Ionization conditions for iontophoretic drug delivery. A revised pKa of lidocaine hydrochloride in aqueous solution at 25°C established by precision conductometry

1996; Elsevier BV; Volume: 141; Issue: 1-2 Linguagem: Inglês

10.1016/0378-5173(96)04616-9

1873-3476

Hans Sjöberg, Kiomars Karami, Per Beronius, Lars‐Olof Sundelöf,

Analytical Chemistry and Sensors

The electrical conductance of lidocaine hydrochloride (LidH+Cl-) in aqueous solution at 25.00°C has been established by precision conductometry over a concentration interval from 0.3 to 6.6 mM. Assuming any ion pairing between the LidH+ and Cl- ions to be negligible, a conductance equation has been derived in which the equilibrium between LidH +, Lid and H + is considered. This equation involves the dissociation constant of LidH+, Ka, and the limiting molar conductivity of LidH-, ⋌o(LidH +), as adjustable parameters. The mobility correction factor used to correct the mobility of the ions for ion atmosphere effects is in accord with the conductance function of Fuoss, Hsia, and Fernandez-Prini (FHFP equation). A computer program was developed to find the values of Ka and ⋌o(LidH +) resulting in the best fit of the conductance equation to the experimental points (minimum standard deviation between experimental and computed A-values). With the distance parameter set equal to the Bjerrum radius, q = 0.357 nm, we obtained pKa(LidH+) = 7.16(molarity scale), λ0(LidH+) = 17.87 cm2Ω−1 mol−1. Our pKa- value is 0.7 units lower than the previously reported potentiometrically determined value, 7.85.