Wallschläger Dirk, Stadey Christopher J
Environmental & Resource Sciences Program, Trent University, 1600 West Bank Drive, Peterborough, ON K9J 7B8, Canada.
Anal Chem. 2007 May 15;79(10):3873-80. doi: 10.1021/ac070061g. Epub 2007 Apr 17.
Although it has long been known that soluble arsenic-sulfur (As-S) compounds exist in sulfidic waters and may play significant roles in several important processes in the biogeochemical arsenic cycle, no suitable analytical methods exist for their determination. We provide evidence that the four homologue (oxy)thioarsenates, mono-, di-, tri-, and tetrathioarsenate (AsO3S3-, AsO2S23-, AsOS33- and AsS43-), can be formed in geochemical model reactions between arsenite and sulfide under anoxic conditions (through currently unknown reaction mechanisms) and that these compounds appear to be major As species in natural sulfidic waters. These As-S species are quantified by anion-exchange chromatography-inductively coupled plasma mass spectrometry (AEC-ICPMS) with instrumental detection limits of approximately 0.1 nmol of As L(-1) in undiluted samples; arsenite, arsenate, and monomethylarsenate are quantified as well, but dimethylarsenate cannot be analyzed by this technique. Sulfur in the eluting peaks can be measured as SO+ with detection limits of approximately 0.1 micromol of S L(-1). The (oxy)thioarsenates were synthesized in solution and characterized by electrospray-tandem mass spectrometry (ES-MS-MS). In geochemical model solutions, we confirmed that both the AEC-ICPMS retention times and the ES-MS-MS spectra of the reaction products of sulfide and arsenite matched the synthesized (oxy)thioarsenate standards; for natural waters, the mass spectrometric confirmation was unsuccessful, due to matrix interferences.
尽管长期以来人们都知道可溶性砷 - 硫（As - S）化合物存在于含硫水体中，并且可能在生物地球化学砷循环的几个重要过程中发挥重要作用，但目前尚无合适的分析方法来测定它们。我们提供的证据表明，四种同系（氧）硫代砷酸盐，即一硫代砷酸盐、二硫代砷酸盐、三硫代砷酸盐和四硫代砷酸盐（AsO₃S₃⁻、AsO₂S₂³⁻、AsOS₃³⁻和AsS₄³⁻），可以在缺氧条件下亚砷酸盐与硫化物之间的地球化学模型反应中形成（通过目前未知的反应机制），并且这些化合物似乎是天然含硫水体中的主要砷物种。这些As - S物种通过阴离子交换色谱 - 电感耦合等离子体质谱法（AEC - ICPMS）进行定量，未稀释样品中砷的仪器检测限约为0.1 nmol L⁻¹；亚砷酸盐、砷酸盐和一甲基砷酸盐也可进行定量，但二甲基砷酸盐不能用该技术分析。洗脱峰中的硫可以通过SO⁺进行测量，检测限约为0.1 μmol S L⁻¹。（氧）硫代砷酸盐在溶液中合成，并通过电喷雾串联质谱法（ES - MS - MS）进行表征。在地球化学模型溶液中，我们证实硫化物和亚砷酸盐反应产物的AEC - ICPMS保留时间和ES - MS - MS光谱与合成的（氧）硫代砷酸盐标准品相匹配；对于天然水体，由于基质干扰，质谱确认未成功。
