Master Thesis

Solid phase extraction: A new method for stabilization and enrichment of thioarsenates?

Valentina Misiari (03/2015-11/2015)

Support: Britta Planer-Friedrich, Maria Ullrich

Thioarsenates are ubiquitous in sulfidic environments and their occurrence has also been confirmed in iron-rich sulfidic systems. However, their preservation in iron-rich samples without precipitation and species transformation is still a challenging task. A new stabilization method for samples containing thioarsenates was tested in the laboratory using the anionexchange resin AG2-X8 and standard solutions of arsenic and sulfur species. The AG2-X8 resin was successfully used to retain anions such as thiosulfate, sulfate, arsenate, monothioarsenate and trithioarsenate, achieving retentions of 95 to 100 %. The retained species could then be eluted qualitatively and quantitatively using 0.5 M salicylate achieving recoveries between 89 and 103 %. Cationic iron and most of the uncharged arsenite passed through the resin without binding as predicted. However, in the presence of excess free sulfide, arsenite was partially retained on the resin, presumably due to sorption via sulfide bridging to the organic resin material. Nevertheless, the retention and recovery of other species was not affected by this effect. The developed method was tested for preservation of natural samples from mineral springs in the Czech Republic. The low shares of thioarsenates detected, led to quantification problems. Moreover, the transfer time of 1 day between loading and elution of the resin, cast doubts on species conversions that may happened during that time, which therefore remains open for further tests. Despite the shortcomings, it could be confirmed that no species transformations were observed during storage of the loaded resin from first elution day until day 6.