Bachelor Thesis

Due to differences in toxicity, an accurate determination of the occurrence of different inorganic arsenic species in natural waters is of great importance. In the current study, different preservation techniques were tested for their efficiency to prevent arsenic species transformation by adsorption, precipitation and redox reactions in iron- and sulfide-rich synthetic and natural water samples. Natural water samples were collected from mineral waters and a swamp in the Czech Republic and analyzed by ICP‑MS for total concentrations and IC‑ICP‑MS for arsenic speciation. Iron and sulfide concentrations ranged from 26 µg/L to 35 mg/L and 0,00 to 0,53 mg/L, respectively, arsenic from 2 to 380 µg/L, with arsenite and arsenate being detectable in all of the 40 springs; thioarsenates were found in Frantiskovy Lazne exclusively. Synthetic waters were prepared in the laboratory containing arsenite, arsenate or monothioarsenate as well as iron and sulfide in concentrations comparable to those measured in the natural samples. The stability of arsenic species was found to decrease significantly with increasing iron concentrations. Flash freezing which best preserves arsenic-sulfur speciation in low-iron waters, led to significant loss of dissolved arsenic by adsorption onto iron precipitates. Removing iron prior to freezing by using cation exchangers was discarded because of arsenate adsorbing onto sorbed iron. Best results for both natural and synthetic samples were achieved by using hydrochloric acid (HCl) combined with dark storage or by adding ethylendinitrilotetraacetic acid (EDTA). Preservation of thioarsenates was problematic in both cases. While only monothioarsenate was detected in HCl-stabilized samples, EDTA seemed to preserve dithioarsenate. However, additional detection of trithioarsenate after 2 weeks of storage raised the questions whether thioarsenates formed artificially in EDTA-preserved samples.