Determination of (Oxy)thioarsenates in Sulfidic Waters

Abstract

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.

Pyrobaculum yellowstonensis Strain WP30 Respires on Elemental Sulfur and/or Arsenate in Circumneutral Sulfidic Geothermal Sediments of Yellowstone National Park

“…Samples for arsenic speciation analysis were thawed in an anaerobic hood (95% N 2 , 5% H 2 atmosphere) to minimize oxidation. Arsenite, arsenate, and thioarsenates were detected by anion-exchange chromatography (Dionex ICS-3000 SP, AG16/AS16 IonPac column) coupled to inductively coupled plasma mass spectrometry (XSeries2; Thermo Fisher) (AEC-ICP-MS) (28,29).…”

High-resolution two-dimensional quantitative analysis of phosphorus, vanadium and arsenic, and qualitative analysis of sulfide, in a freshwater sediment

“…[43] Recently, evidence for the analogous intermediates of (oxy)thioarsenates (AsO x S 3− 3−x , x = 0-3) has been presented. [44] Should the rate and scavenging behaviour be analogous to that observed for molybdenum, arsenic transformations at sulfidic microniches may be significant, compared with the average for that depth. Helz et al [43] have raised the possibility that Mo fixation within highly sulfidic microenvironments (such as those observed by Widerlund and Davison [25] and MotelicaHeino et al [45] ) may be misinterpreted as fixation at low sulfide concentrations within the bulk sediment.…”

Arsenic binding to organic and inorganic sulfur species during microbial sulfate reduction: a sediment flow-through reactor experiment

“…Visually similar fits were further evaluated by selecting those with the lowest R-factor values, and permutations were tested by selecting the combinations that lowered the reduced Chi-square (x red 2 ) values by at least 20 %, which was deemed a significant improvement. The suite of reference materials included was as follows: (i) the sodium salts of As III and As V (Sigma-Aldrich), MTAs V and TTAs V prepared according to Wallschläger and Stadey, [35] (ii) the minerals AsS (s) (Sigma-Aldrich), As 2 S 3(s) (Alfa-Aesar), nano-crystalline As 2 S 3(s) (digitised from Helz et al [36] ), scorodite and arsenopyrite (D. Testemale, pers. comm.…”