Accademia Delle Scienze dell'istituto di Bologna, Via Zamboni, 31, 40126 Bologna, Italy.
J Chromatogr A. 2013 Nov 1;1314:106-14. doi: 10.1016/j.chroma.2013.09.013. Epub 2013 Sep 12.
Many physical phenomena are affected by the structure of water interfaces, yet it remains an active and controversial subject. A great deal of recent theoretical endeavour and computer simulations question the validity of the Onsager Samaras theory of the ion-free interface between an electrolyte solution and an hydrophobic surface. Experimental results play a crucial role in assessing the legitimacy of the theories. Experimental data are scarce, while simulation results suggest an increasing surface affinity of ions with increasing chaotropic character, in dramatic contradiction to the classical view. Chromatography is a powerful separative technique, but we originally used it as a tool to detect the adsorption of chloride electrolytes and sodium electrolytes, strongly expected to shun any dielectric boundary, onto an hydrophobic surface, and to rank ions according to their adsorbophilicities. Frontal analysis gave unequivocal experimental evidence to this unexpected phenomenon and it was used to quantify it. The infinite dilution equilibrium constants for adsorption of kosmotropes and chaotropes onto the interface were obtained and contrasted to the Jones-Dole B viscosity coefficients, that is a common quantifier of the Hofmeister effect. It is clear that (i) the more chaotropic the ion is, the more it contributes to the global adsorbophilicity of the electrolyte; (ii) the influence of the variable anion is more than twofold that of the variable cation, thereby confirming a robust observation in many other physical systems. Standard free energy of adsorption for each electrolyte was calculated and its reliability was commented upon. The central issue in this paper is the effective and ascertained adsorption of electrolytes onto an hydrophobic surface and the fact that the adsorbophilicity of an electrolyte may be inferred from its position in the Hofmeister series.
许多物理现象都受到水界面结构的影响，但这仍然是一个活跃且有争议的课题。最近的大量理论研究和计算机模拟对电解质溶液和疏水表面之间无离子的 Onsager-Samaras 理论的有效性提出了质疑。实验结果在评估理论的合法性方面起着至关重要的作用。实验数据稀缺，而模拟结果表明，随着离质体的离质特征增加，离子对表面的亲和力也会增加，这与经典观点形成了鲜明的对比。色谱法是一种强大的分离技术，但我们最初将其用作检测氯化物电解质和钠电解质吸附到疏水表面的工具，这两种电解质都强烈地避免任何介电边界，并根据其吸附亲合性对离子进行排序。前沿分析为这一意外现象提供了明确的实验证据，并对其进行了量化。我们获得了离质体和离质体在界面上无限稀释吸附的平衡常数，并将其与 Jones-Dole B 粘度系数进行了对比，后者是 Hofmeister 效应的常用定量指标。很明显：(i) 离子的离质特征越强，它对电解质整体吸附亲合性的贡献就越大；(ii) 可变阴离子的影响是可变阳离子的两倍多，从而在许多其他物理系统中证实了这一稳健的观察结果。我们计算了每个电解质的标准吸附自由能，并对其可靠性进行了评论。本文的核心问题是电解质有效且确定地吸附到疏水表面上，以及可以从 Hofmeister 序列中推断出电解质的吸附亲合性。
