On-site speciation of inorganic arsenic using a flow-type electrodialytic ion-transfer device with selective arsenite...

Speciation analysis of inorganic arsenic is essential for assessing its toxicity because its chemical form significantly affects its behavior and health risks. However, post-sampling changes, such as oxidation during storage, treatment, and analysis, often hinder the accurate quantification of arsenite and arsenate. Here, we developed a flow-type electrodialytic ion-transfer device (ITD) capable of immediate on-site separation of arsenic species, particularly targeting the selective isolation of highly toxic arsenite. The ITD comprises donor, acceptor, and isolator channels, and it enables efficient separation of arsenite and arsenate by applying 100 V across the system. Arsenite is selectively transferred through the donor channel, while arsenate migrates into the acceptor channel along with strongly acidic anions, such as chloride and sulfate. Using this approach, we found that the arsenite/arsenate ratio in a hot spring water sample significantly differed between immediate on-site separation and separation after 1 month storage, underscoring the risk of arsenite oxidation. The trace arsenic species in hot spring water were quantified by hydride-generation atomic absorption spectrometry, while coupling the ITD with ion-exclusion chromatography facilitated the separation of arsenite and silicate in brine, with desalination effectively achieved by the ITD. These results demonstrate that the ITD offers a practical strategy for preserving the arsenic speciation at the point of sampling and improves the analytical reliability of complex aqueous matrices.