preparation-dmmtav-dmdtav-using-dmav-for-environmental-applications

Preparation of DMMTAV and DMDTAV Using DMAV for Environmental Applications: Synthesis, Purification, and Confirmation

Dimethylated thioarsenicals such as dimethylmonothioarsinic acid (DMMTAV) and dimethyldithioarsinic acid (DMDTAV), which are produced by the metabolic ...

Yonsei University

This study was undertaken to ascertain optimal methods of sampling, preserving, separating, and analyzing arsenic species in potentially contaminated waters. Arsenic species are readily transformed in nature by slight changes in conditions. Each species has a different toxicity and mobility. The conventional field sampling method using filters of 0.45 microm in size could overestimate the dissolved arsenic concentrations, as passing suspended particles that can act as a sink or source of arsenic depending on the site condition. For arsenic species in neutral pH and iron-poor waters, the precipitation can be stable for up to 3 days without any treatment, but for longer periods, a preservative, such as phosphoric acid, is required. Also, the analytical procedure must be selected carefully because the levels and hydride generation efficiencies of arsenic in different species can vary, even for the same amount of arsenic. For arsenic speciation in samples that also include organic species, a hybrid high-performance liquid chromatography (HPLC) column and inductively coupled plasma mass spectrometry (ICP-MS) gave the best resolution and lowest detection limits. However, the procedure using a solid phase extraction (SPE) cartridge can be used economically and conveniently for analyzing samples containing only inorganic arsenic species, such as groundwater, especially that related to mine activity.

An assessment of sampling, preservation, and analytical procedures for arsenic speciation in potentially contaminated waters.

Dimethylmonothioarsinic acid (DMMTA) is a highly toxic, thiolated analogue of dimethylarsinic acid (DMA). In comparison, a further thiolated analogue, dimethyldithioarsinic acid (DMDTA), and DMAboth exhibit lower toxicity. To understand the environmental conditions responsible for forming DMMTA, the kinetics of DMAthiolation are examined. The thiolation of DMAis pH-dependent and consists of two consecutive first-order reactions under excess sulfide conditions. The first thiolation of DMAto form DMMTAis faster than the second one to DMDTA. DMMTAis therefore an intermediate. The first reaction is first-order in HS at pH 6.0 and 20 °C; therefore, the overall reaction is second-order and the rate coefficient in this condition is 0.0780 Ms. The rate coefficient significantly decreases at pH 8.0, indicating that HS(aq) triggers the thiolation of DMA. The second reaction rate is significantly decreased at pH 2.5; therefore, reaction under strongly acidic conditions leads to accumulation of highly toxic DMMTAin the early stages of thiolation. The transformation of DMDTAto DMMTAis catalyzed in the presence of ferric iron. Formation of DMMTAshould be considered when assessing risk posed by arsenic under sulfidic or sulfate reducing conditions.

Article	Year
An assessment of sampling, preservation, and analytical procedures for arsenic speciation in potentially contaminated waters. Environmental geochemistry and health\| PubMed ID: 17505895	2007
Kinetics of Dimethylated Thioarsenicals and the Formation of Highly Toxic Dimethylmonothioarsinic Acid in Environment. Environmental science & technology\| PubMed ID: 27701855	2016

Youn-Tae Kim

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