Fisk Jonathan D, Batten Robin, Jones Glenn, O'Reilly Josephine P, Shaw Andrew M
School of Biological and Chemical Sciences, University of Exeter, Stocker Road, Exeter EX4 4QD, UK.
J Phys Chem B. 2005 Aug 4;109(30):14475-80. doi: 10.1021/jp051211z.
The pH-dependent adsorption isotherms for the charged chromophore crystal violet, CV(+), have been measured with three different bases by a free-running cavity implementation of evanescent wave cavity ring-down spectroscopy. The ratio of the maximal absorbance measurements at pH 5.10 and 9.05 is consistent with a Q2:Q3 silanol site ratio of 72.8:27.2. The adsorption isotherms have been interpreted in terms a cooperative binding adsorption allowing more than one ionic species to bind to each silanol group. The surface concentration is consistent with a silanol charge density of 1.92 +/- 0.55 nm(-2) and a total neutralized interface layer structure extending 9 nm from the surface. Binding constants and stoichiometric coefficients are derived for CV(+) to both the Q2 and Q3 sites. A variation of the adsorption isotherm with base is observed so that the isotherm at pH 9.05 adjusted with ammonium hydroxide sets up a competitive acid-base equilibrium with the SiOH groups with only 49% of the surface silanol sites dissociated. The implications for functionalized surfaces in chromatography are discussed.
通过消逝波腔衰荡光谱的自由运行腔实现方式，用三种不同的碱测量了带电荷发色团结晶紫（CV(+)）的pH依赖吸附等温线。在pH 5.10和9.05下最大吸光度测量值的比值与Q2:Q3硅醇位点比例72.8:27.2一致。吸附等温线已根据允许不止一种离子物种与每个硅醇基团结合的协同结合吸附进行了解释。表面浓度与1.92 +/- 0.55 nm(-2)的硅醇电荷密度以及从表面延伸9 nm的完全中和的界面层结构一致。推导了CV(+)与Q2和Q3位点的结合常数和化学计量系数。观察到吸附等温线随碱的变化，因此用氢氧化铵调节至pH 9.05时的等温线与SiOH基团建立了竞争酸碱平衡，只有49%的表面硅醇位点解离。讨论了其对色谱中功能化表面的影响。
