Beak Douglas G, Wilkin Richard T, Ford Robert G, Kelly Shelly D
National Risk Management Research Laboratory, U.S. Environmental Protection Agency, 919 Kerr Research Drive, Ada, Oklahoma 74820, USA.
Environ Sci Technol. 2008 Mar 1;42(5):1643-50. doi: 10.1021/es071858s.
Both thioarsenites and thioarsenates have been demonstrated to exist in sulfidic waters, yet there is uncertainty regarding the geochemical conditions that govern the formation of these arsenic species. The purpose of this research was to use advanced spectroscopy techniques, speciation modeling, and chromatography to elucidate the chemical speciation of arsenic in sulfidic solutions initially containing arsenite and sulfide. Results of X-ray absorption spectroscopy (XAS) show that experimental solutions contained mixtures of arsenite and thioarsenites with increasing substitution of sulfur for oxygen on arsenic as the sulfide concentration increased. Experimental samples showed no evidence of polymeric arsenic species, or transformation of thioarsenites to thioarsenates. The arsenic speciation measured using XAS was similar to predictions obtained from a thermodynamic model for arsenic speciation, excluding thioarsenate species in sulfidic systems. Our data cast some doubt on the application of chromatographic methods for determining thioarsenates and thioarsenites (or mixtures) in natural waters in cases where the arsenic oxidation state cannot be independently verified. The same chromatographic peak positions proposed for thioarsenates can be explained bythioarsenite species. Furthermore, sample dilution was shown to change the species distribution and care should be taken to avoid sample dilution prior to chromatographic analysis.
硫代亚砷酸盐和硫代砷酸盐已被证明存在于含硫水中，然而，关于控制这些砷物种形成的地球化学条件仍存在不确定性。本研究的目的是利用先进的光谱技术、形态建模和色谱法来阐明初始含有亚砷酸盐和硫化物的含硫溶液中砷的化学形态。X射线吸收光谱（XAS）结果表明，实验溶液中含有亚砷酸盐和硫代亚砷酸盐的混合物，随着硫化物浓度的增加，砷上的硫对氧的取代也增加。实验样品没有显示出聚合砷物种的证据，也没有显示出硫代亚砷酸盐向硫代砷酸盐的转化。使用XAS测量的砷形态与从砷形态热力学模型获得的数据相似，但不包括含硫体系中的硫代砷酸盐物种。我们的数据对色谱法在无法独立验证砷氧化态的情况下用于测定天然水中硫代砷酸盐和硫代亚砷酸盐（或混合物）的适用性提出了一些质疑。硫代亚砷酸盐物种可以解释为硫代砷酸盐所提出的相同色谱峰位置。此外，样品稀释会改变物种分布，在进行色谱分析之前应注意避免样品稀释。
