De Marco Roland, Pejcic Bobby, Prince Kathryn, van Riessen Arie
Department of Applied Chemistry, Curtin University of Technology, GPO Box U 1987, Perth, Western Australia, 6845, Australia.
Analyst. 2003 Jun;128(6):742-9. doi: 10.1039/b212914k.
X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), rotating disc electrode-electrochemical impedance spectroscopy (RDE-EIS) and synchrotron radiation-grazing incidence X-ray diffraction (SR-GIXRD) have been used to study the response mechanism of the mercury(II) chalcogenide ion-selective electrode (ISE) in saline media. XPS and SIMS have shown that the chalcogenide surface is poisoned by silver chloride, or a mixture of silver halides, on continuous exposure to synthetic and real seawater. Significantly, the in-situ SR-GIXRD study demonstrated that electrode fouling in synthetic seawater is linked to the formation of poorly crystalline or amorphous silver chloride, and that the low level of free mercury(II) in a calibration buffer (i.e., 10(-14) M) is able to undergo metathesis with silver(II) sulfide in the membrane generating mercury(II) sulfide. Significantly, the results of this detailed surface study have shown that silver chloride fouling of the electrode is ameliorated in real seawater comprising natural organic ligands, and this has been attributed to the peptization of silver chloride by the surfactant-like nature of seawater ligands at pH 8. RDE-EIS aging studies have revealed that the chalcogenide membrane experiences a sluggish charge transfer reaction in seawater, and contrary to a previous report for a static electrode, the seawater matrix does not passivate the RDE. The results of this XPS, SIMS, RDE-EIS and SR-GIXRD study have elucidated the response mechanism of the mercury(II) ISE in saline media.
X射线光电子能谱（XPS）、二次离子质谱（SIMS）、旋转圆盘电极-电化学阻抗谱（RDE-EIS）和同步辐射掠入射X射线衍射（SR-GIXRD）已被用于研究硫属汞（II）离子选择性电极（ISE）在含盐介质中的响应机制。XPS和SIMS表明，在持续暴露于合成海水和实际海水时，硫属化物表面会被氯化银或卤化银混合物中毒。重要的是，原位SR-GIXRD研究表明，合成海水中的电极污染与形成结晶性差或无定形的氯化银有关，并且校准缓冲液中低水平的游离汞（II）（即10^(-14) M）能够与膜中的硫化银发生复分解反应生成硫化汞。重要的是，这项详细表面研究的结果表明，在含有天然有机配体的实际海水中，电极的氯化银污染得到改善，这归因于海水配体在pH 8时类似表面活性剂的性质使氯化银胶溶。RDE-EIS老化研究表明，硫属化物膜在海水中经历缓慢的电荷转移反应，与之前关于静态电极的报道相反，海水基质不会使RDE钝化。这项XPS、SIMS、RDE-EIS和SR-GIXRD研究的结果阐明了汞（II）ISE在含盐介质中的响应机制。
