Bura-Nakić Elvira, Krznarić Damir, Jurasin Darija, Helz George R, Ciglenecki Irena
Center for Marine and Environmental Research, Rudjer Bosković Institute, Bijenicka 54, 10 000 Zagreb, Croatia.
Anal Chim Acta. 2007 Jun 26;594(1):44-51. doi: 10.1016/j.aca.2007.04.065. Epub 2007 May 6.
Voltammetric scans in sulfidic natural waters often reveal reduction peaks in the range -0.9 to -1.35 V versus Ag/AgCl. These peaks have been attributed to iron sulfide complexes or clusters. However, sols containing CuS nanoparticles now also are known to produce reduction peaks in this range. Here we investigate the voltammetric behavior of two additional metal sulfides at the Hg electrode in 0.55 M NaCl + 0.03 M NaHCO3 electrolyte, pH=8.5. We show that Pb and Hg sulfides, either as suspended powders or as precipitated nanoparticles, also yield cathodic peaks between -0.9 and -1.35 V, similar to peaks obtained with CuS and FeS. For precipitated nanoparticles, the position and shape of these reduction peaks change with ageing. Freshly formed nanoparticles produce less negative reduction peaks than aged nanoparticles. Peaks from aged nanoparticles often consist of two or more superimposed reduction peaks. When all other experimental parameters are held constant, the amount of nanoparticle analyte accumulated on the electrode increases with the amount of ageing (< or = 1 h). Addition of EDTA or acidification followed by purging can be used to distinguish PbS nanoparticles and Fe sulfide clusters from CuS and HgS nanoparticles or from colloidal S. This test was applied to interpret -0.9 to -1.35 V reduction peaks observed in two meromictic lakes. In conjunction with other evidence, this test suggests that FeS clusters are present in one case whereas colloidal S is present in the other. Interpreting -0.9 to -1.35 V voltammetric peaks observed in sulfidic natural waters requires caution, but these peaks are potentially rich sources of information about trace metal speciation.
在含硫的天然水体中进行伏安扫描时，相对于Ag/AgCl参比电极，常常会在-0.9至-1.35 V范围内出现还原峰。这些峰被认为是由硫化铁络合物或簇状物引起的。然而，现在已知含有硫化铜纳米颗粒的溶胶在该范围内也会产生还原峰。在此，我们研究了另外两种金属硫化物在0.55 M NaCl + 0.03 M NaHCO3电解液（pH = 8.5）中汞电极上的伏安行为。我们发现，硫化铅和硫化汞，无论是以悬浮粉末形式还是沉淀纳米颗粒形式存在，在-0.9至-1.35 V之间也会产生阴极峰，这与硫化铜和硫化铁产生的峰类似。对于沉淀的纳米颗粒，这些还原峰的位置和形状会随着老化而变化。新形成的纳米颗粒产生的还原峰负电位比老化后的纳米颗粒要小。老化纳米颗粒产生的峰通常由两个或更多叠加的还原峰组成。当所有其他实验参数保持恒定时，电极上积累的纳米颗粒分析物的量会随着老化时间（≤1小时）的增加而增加。添加乙二胺四乙酸（EDTA）或酸化后吹扫可用于区分硫化铅纳米颗粒和硫化铁簇与硫化铜、硫化汞纳米颗粒或胶体硫。该测试被用于解释在两个半混合湖（meromictic lakes）中观察到的-0.9至-1.35 V的还原峰。结合其他证据，该测试表明在一种情况下存在硫化铁簇，而在另一种情况下存在胶体硫。解释在含硫天然水体中观察到的-0.9至-1.35 V伏安峰需要谨慎，但这些峰可能是有关痕量金属形态的丰富信息来源。
