Discipline: Chemistry and Chemical Sciences
Subcategory: Chemistry (not Biochemistry)
Akeena Harper - Voorhees College
Co-Author(s): Denzel Bolden and Jianye Zhang, Voorhees College, Denmark, SC
Arsenic exists in environment in various forms and its toxicity is strongly related to its exact chemical form (speciation). Inorganic forms of arsenic, such as arsenite and arsenate, are usually considered more toxic than organic arsenic species (such as monomethylarsonic acid (MMAA), and dimethylarsinic acid (DMAA)). Therefore, the speciation of arsenic is critical when evaluating the toxicity of arsenic in environment. Chromatographic separation techniques such as liquid chromatography (LC) or ion chromatography (IC), coupled with sensitive mass spectrometry (MS), are the most popular for the quantitative detection of arsenic species. Thioarsenics, a class of inorganic arsenic-sulfur complexes, have recently been found in (sulfidic) environments with high sulfide levels, such as landfills and hot springs, mostly using ion chromatographic (IC) based methods with inductively coupled plasma mass spectrometer (ICPMS) as the detector. But the simultaneous, particularly molecular, detection of thioarsenic species and other common arsenic species has not been reported. The objective of this study was to develop a method for the comprehensive analysis of arsenic species in environments with high level of sulfide.
Thioarsenic compounds were synthesized and obtained in the lab following the method described in reference. Both ion chromatography (IC) and high performance liquid chromatography (HPLC) were used to explore the separation of arsenic species, which include arsenite, arsenate, MMAA, DMAA, and thioarsenic species. It is hypothesized that by adjusting the chromatographic conditions and employing appropriate separation column, thioarsenic species and the other four common arsenic species can be successfully separated and detected.
Currently, our results show that ion chromatography with conductivity detector can successfully separate and detect thioarsenic species. In our samples, four thioarsenic species, monothioarsenate, dithioarsenate, trithioarsenate, and tetrathioarsenate have been separated and detected. Arsenite, arsenate, MMAA and DMAA has been successfully separated on WAX-1 mixed-mode column and anion exchange column with phosphate buffer or ammonium acetate buffer. Thioarsenates can also be separated on anion exchange column but with long retention time.
Future research will focus on the transfer of the HPLC method to LC/MS method and the optimization of analysis of arsenic and thioarsenic species.
Funder Acknowledgement(s): This study was supported by the NSF HBCU-UP RIA Award (HRD-1411031).
Faculty Advisor: Jianye Zhang, firstname.lastname@example.org
Role: I did the HPLC method development using WAX-1 and anion exchange columns.