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首页> 外文期刊>Electroanalysis >Low frequency square-wave voltammetry of weak acids at platinum Microelectrodes
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Low frequency square-wave voltammetry of weak acids at platinum Microelectrodes

机译：铂微电极上弱酸的低频方波伏安法

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摘要

The reduction process of monoprotic weak acids (lactic and acetic acid, and dihydrogen phosphate ion) and mixtures of a strong and a weak acid (perchloric and one of the above weak acids) have been investigated by square-wave voltammetry (SWV) at a platinum microelectrode 12.5 mu m radius. The SW measurements have been performed at low frequencies (i.e., 3 Hz), where the heterogeneous electron transfer process, involving hydrogen evolution (2H(+) + 2e = H-2), is essentially reversible, and non-planar diffusion conditions prevail in the mass transport. Under these conditions, the forward and the reverse current-potential profiles are sigmoidal, whereas the net current-potential profile is peak shaped. The influence of dissociation constant and analytical concentration of the weak acid on the features of the square-wave voltammograms has been examined in detail. In general, both these characteristics of the weak acids affect the square-wave parameters peak potential (E-P), width at half height (W-1/2) and net peak current (i(p)) in a complex manner. Their dependence on concentration is due to the 2:1 stoichiometry of the heterogeneous electron transfer, while the dissociation constant contribution arises because of the CE mechanism involved in the overall electrode process. The kinetic of the homogeneous reaction has been investigated by the use of the forward current plateau (achieved by the end of the sweep) along with a theoretical equation. Mixtures of a strong and a weak acid can provide one or two waves, depending on the acid strength and on the analytical concentration of each acid. Peak potential differences of about 80 mV are needed to discern two peaks. Calibration plots, examined for all the weak acids, have shown that linearity may exist only over relatively small concentration ranges.
机译：单质子质弱酸（乳酸和乙酸，磷酸二氢根离子）以及强酸和弱酸（高氯酸和上面的一种弱酸）的混合物的还原过程已通过方波伏安法（SWV）在室温下研究。半径为12.5微米的铂微电极。 SW测量是在低频（即3 Hz）下进行的，其中涉及氢释放（2H（+）+ 2e = H-2）的异质电子转移过程基本上是可逆的，并且存在非平面扩散条件在大众运输中。在这些条件下，正向和反向电流电势曲线为S型，而净电流电势曲线为峰形。详细研究了解离常数和弱酸的分析浓度对方波伏安图特征的影响。通常，弱酸的这两种特性都会以复杂的方式影响方波参数的峰电位（E-P），半峰宽（W-1 / 2）和净峰电流（i（p））。它们对浓度的依赖性是由于异质电子转移的化学计量比为2：1，而解离常数的贡献是由于整个电极过程中涉及的CE机理而产生的。均相反应的动力学已通过使用正向电流平稳段（在扫描结束时实现）以及理论方程进行了研究。强酸和弱酸的混合物可产生一波或两波，这取决于酸强度和每种酸的分析浓度。需要大约80 mV的峰电位差来识别两个峰。对所有弱酸进行的校正图表明，线性可能仅在相对较小的浓度范围内存在。

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