Department of Chemistry, University of Pittsburgh, 219 Parkman Avenue, Pittsburgh, Pennsylvania 15260, United States.
Anal Chem. 2015;87(10):5348-55. doi: 10.1021/acs.analchem.5b00644. Epub 2015 May 8.
Cation-exchange extraction of polypeptide protamine from water into an ionophore-based polymeric membrane has been hypothesized as the origin of a potentiometric sensor response to this important heparin antidote. Here, we apply ion-transfer voltammetry not only to confirm protamine extraction into ionophore-doped polymeric membranes but also to reveal protamine adsorption at the membrane/water interface. Protamine adsorption is thermodynamically more favorable than protamine extraction as shown by cyclic voltammetry at plasticized poly(vinyl chloride) membranes containing dinonylnaphthalenesulfonate as a protamine-selective ionophore. Reversible adsorption of protamine at low concentrations down to 0.038 μg/mL is demonstrated by stripping voltammetry. Adsorptive preconcentration of protamine at the membrane/water interface is quantitatively modeled by using the Frumkin adsorption isotherm. We apply this model to ensure that stripping voltammograms are based on desorption of all protamine molecules that are transferred across the interface during a preconcentration step. In comparison to adsorption, voltammetric extraction of protamine requires ∼0.2 V more negative potentials, where a potentiometric super-Nernstian response to protamine is also observed. This agreement confirms that the potentiometric protamine response is based on protamine extraction. The voltammetrically reversible protamine extraction results in an apparently irreversible potentiometric response to protamine because back-extraction of protamine from the membrane extremely slows down at the mixed potential based on cation-exchange extraction of protamine. Significantly, this study demonstrates the advantages of ion-transfer voltammetry over potentiometry to quantitatively and mechanistically assess protamine transfer at ionophore-based polymeric membranes as foundation for reversible, selective, and sensitive detection of protamine.
已假设阳离子交换从水中提取多肽鱼精蛋白进入基于离子载体的聚合物膜是这种重要的肝素解毒剂产生电位传感器响应的起源。在这里，我们不仅应用离子转移伏安法来确认鱼精蛋白被提取到掺杂有离子载体的聚合物膜中，还揭示了鱼精蛋白在膜/水界面的吸附。正如含有作为鱼精蛋白选择性离子载体的二壬基萘磺酸的增塑聚氯乙烯膜中的循环伏安法所示，鱼精蛋白的吸附在热力学上比鱼精蛋白的提取更有利。通过剥离伏安法证明了在低浓度下（低至 0.038 μg/mL）鱼精蛋白的可逆吸附。通过使用 Frumkin 吸附等温线对膜/水界面处鱼精蛋白的吸附性预浓缩进行定量建模。我们应用此模型来确保剥离伏安图是基于在预浓缩步骤中跨越界面转移的所有鱼精蛋白分子的解吸。与吸附相比，鱼精蛋白的伏安萃取需要更负约 0.2 V 的电位，在该电位下也观察到对鱼精蛋白的超 Nernst 电位响应。这种一致性证实了电位测定的鱼精蛋白响应基于鱼精蛋白的提取。由于基于阳离子交换提取鱼精蛋白，鱼精蛋白的电化学可逆提取导致对鱼精蛋白的显然不可逆的电位响应，从而从膜中反向提取鱼精蛋白极其缓慢。重要的是，这项研究证明了与离子转移伏安法相比，离子选择性和敏感检测鱼精蛋白的可逆性，选择性和敏感性的基础是基于离子载体的聚合物膜中鱼精蛋白转移的定量和机理评估，离子转移伏安法具有优势。
