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首页> 外文期刊>Marine Chemistry >Comparison and combined use of linear and non-linear fitting for the estimation of complexing parameters from metal titrations of estuarine samples by CLE/AdCSV
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Comparison and combined use of linear and non-linear fitting for the estimation of complexing parameters from metal titrations of estuarine samples by CLE/AdCSV

机译：线性拟合和非线性拟合的比较和组合使用，用于通过CLE / AdCSV从河口样品的金属滴定估算络合参数

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摘要

Despite the need to determine the concentration and conditional stability constants (K') of natural ligands, we are far from achieving a consensus about the mathematical procedure to use with metal titrations due to the complexity of the samples and the wide range of fitting procedures and problems associated with the selection of the sensitivity (S) of the method. Here, we used Competitive Ligand Exchange/Adsorptive Cathodic Stripping Voltammetry (CLE/AdCSV) empiric data from estuarine waters and computer generated titration sets to compare linear methods with iterative correction of S with non-linear fitting adding S as a parameter. We demonstrate for the first time that, independent of the fitting procedure, S cannot be retrieved if all the ligands present in the sample are not included in the speciation model. We also investigated the variables, apart from analytical noise, that can cause flawed non-linear fittings of titration data. Computer generated data under multiple combinations of analytical conditions showed that a long extension of the titration (at least twice the total ligand concentration for estuarine conditions) and an analytical window (as the side coefficient oc') centered below the complexing strength of the natural ligands are essential to produce reliable complexing parameters. We verified, using for the first time a combination of experimental and computer generated data, that faulty estimations of S and K' obtained in empiric titrations of estuarine samples were artifacts of non-linear fitting. Non-linear fitting flaws were caused by a combined effect of the analytical error, the analytical window and the ratio in between the copper concentration and the concentration of the strongest ligands. Here, we recommend for the study of estuarine waters to complement non-linear fitting with iterative linear fitting in order to avoid severe overestimations of S and the conditional stability constant of strong metal ligands.
机译：尽管需要确定天然配体的浓度和条件稳定性常数（K'），但由于样品的复杂性以及广泛的拟合程序和复杂性，我们仍无法就金属滴定使用的数学程序达成共识。与方法灵敏度（S）的选择相关的问题。在这里，我们使用了来自河口水的竞争性配体交换/吸附式阴极溶出伏安法（CLE / AdCSV）经验数据和计算机生成的滴定仪，比较了线性方法和S的迭代校正，并通过非线性拟合添加S作为参数。我们首次证明，如果样品中存在的所有配体未包括在物种形成模型中，则无论拟合过程如何，都无法检索到S。除分析噪声外，我们还研究了可能导致滴定数据非线性拟合有缺陷的变量。在多种分析条件组合下的计算机生成数据显示，滴定的长时间扩展（对于河口条件，至少是配体总浓度的两倍）和分析窗口（作为侧系数oc'）居中于天然配体的复合强度以下对产生可靠的络合参数至关重要。我们首次结合实验数据和计算机生成的数据，验证了在经验性滴定河口样品中获得的S和K'的错误估计是非线性拟合的假象。非线性拟合缺陷是由分析误差，分析窗口以及铜浓度与最强配体浓度之间的比率的综合影响引起的。在这里，我们建议对河口水进行研究，以用迭代线性拟合来补充非线性拟合，以避免S的严重高估和强金属配体的条件稳定性常数。

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