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The relevance of ligand exchange kinetics in the measurement of iron speciation by CLE-AdCSV in seawater

机译：配体交换动力学与海水中CLE-AdCSV测定铁形态的相关性

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CLE-AdCSV (competitive ligand exchange-adsorptive cathodic stripping voltammetry) has proved to be a decisive technique in recognising the key role that organic matter plays in modulating the biogeochemical cycle of iron in aquatic ecosystems. As the method requires equilibrium among all the constituents of the solution before measurements are taken, accurate knowledge of the kinetics of the undergoing ligand exchange is essential. The kinetics of the process has been most frequently described in terms of a dissociative (or Eigen-Wilkins) mechanism, with some authors even claiming that, under such approach, iron complexes would dissociate during CLE so slowly that the method would be invalidated. The complexity of the processes largely exceeding the simple mechanistic description of the Eigen-Wilkins mechanism is discussed on the basis of a broad overview of possible reaction routes. Evidence of the role of matrix components of natural waters is presented and the impossibility of exporting kinetic constants to systems characterised by different molecular mechanics, mostly ignored in previous studies, is highlighted. Experimental evidence obtained from various methodological approaches allows inferring the range of CLE equilibration times to be applied in CLE-AdCSV measurements and further proves that the Eigen-Wilkins mechanism is just one of the many reaction routes applicable in natural waters. Studying iron CLE mechanisms for proposed competing ligands before designing any experiment using CLE-AdCSV is recommended. (C) 2014 Elsevier B.V. All rights reserved.
机译：事实证明，CLE-AdCSV（竞争性配体交换-吸附阴极溶出伏安法）是一种决定性技术，可识别有机物在调节水生生态系统中铁的生物地球化学循环中的关键作用。由于该方法需要在进行测量之前在溶液的所有成分之间保持平衡，因此准确了解正在进行的配体交换的动力学至关重要。该过程的动力学最常以离解（或Eigen-Wilkins）机制来描述，一些作者甚至声称，在这种方法下，铁络合物在CLE期间解离得太慢，以致该方法无效。在可能的反应路线的广泛概述的基础上，讨论了过程的复杂性大大超出了对Eigen-Wilkins机理的简单机械描述。提出了天然水的基质成分的作用的证据，并强调了不可能将动力学常数输出到以不同分子力学为特征的系统的可能性，而在以前的研究中大多数都忽略了这一点。从各种方法学方法获得的实验证据可以推断出在CLE-AdCSV测量中应用CLE平衡时间的范围，并进一步证明Eigen-Wilkins机制只是适用于天然水域的众多反应途径之一。建议在设计任何使用CLE-AdCSV的实验之前，研究拟议的竞争配体的铁CLE机制。 （C）2014 Elsevier B.V.保留所有权利。

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