Maitani Y, Kugo M, Nakagaki M, Nagai T
Department of Pharmaceutics, Hoshi University, Tokyo, Japan.
J Pharm Sci. 1993 Dec;82(12):1245-9. doi: 10.1002/jps.2600821212.
The objectives of this study were to evaluate the size of the diclofenac ion and the electrical behavior of diclofenac salts (DM; M = Li, Na, or K) in ethanol/water mixtures. The molar conductance of DM in aqueous solution was measured in a dilute concentration range of < 10 mol.m-3 at 25 degrees C. The Fuoss-Onsager conductance equation for unassociated electrolytes was used to determine the limiting molar conductance (lambda degrees) of DM. The molar conductivity of DM at a finite concentration was, however, larger than the value calculated by the Fuoss-Onsager limiting law. To correct the difference in the experimental data, two equations were employed to fit the experimental molar conductance of DM. The size of the diclofenac ion was calculated from the limiting molar conductance and compared with the values obtained by the Fedors method and the apparent ionization constant (pKa) of sodium diclofenac in ethanol/water mixture. The Walden products of DM increased up to 20% (w/w) ethanol, but above this concentration of ethanol they decreased. Specific interactions between the ions and solvent are discussed.
本研究的目的是评估双氯芬酸离子的大小以及双氯芬酸盐（DM；M = Li、Na或K）在乙醇/水混合物中的电学行为。在25℃下，在<10 mol·m⁻³的稀浓度范围内测量了DM在水溶液中的摩尔电导率。使用未缔合电解质的福斯-昂萨格电导率方程来确定DM的极限摩尔电导率（λ°）。然而，DM在有限浓度下的摩尔电导率大于通过福斯-昂萨格极限定律计算的值。为了校正实验数据中的差异，采用了两个方程来拟合DM的实验摩尔电导率。根据极限摩尔电导率计算双氯芬酸离子的大小，并与通过费多尔斯方法获得的值以及双氯芬酸钠在乙醇/水混合物中的表观电离常数（pKa）进行比较。DM的瓦尔登乘积在乙醇含量高达20%（w/w）时增加，但在高于此乙醇浓度时降低。讨论了离子与溶剂之间的特定相互作用。
