Martínez V, Maguregui MI, Jiménez RM, Alonso RM. Determination of the pKa values of beta-blockers by automated potentiometric titrations.
J Pharm Biomed Anal 2000;
23:459-68. [PMID:
10933539 DOI:
10.1016/s0731-7085(00)00324-1]
[Citation(s) in RCA: 47] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The acid-base equilibrium constants of the beta-blockers atenolol, oxprenolol, timolol and labetalol were determined by automated potentiometric titrations. The pKa values were obtained in water-rich or water methanol medium (20% MeOH) to obviate the solubility problems associated with the compounds. The initial estimates of pKa values were obtained from Gran's method and then, were refined by the NYTIT and ZETA versions of the LETAGROP computer program. The resultant values were 9.4 (I = 0.1 M KCl, 20% methanol) for atenolol, 9.6 (I = 0.1 M KCl) for oxprenolol, 9.4 (I = 0.1 M KCl, 20% methanol) for timolol and 7.4 and 9.4 (I = 0.1 M KCl) for labetalol. The potentiometric method was found to be accurate and easily applicable. The operational criteria for applying the methodology are indicated.
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