Cadmium-Assisted\nPhotochemical Vapor Generation of\nArsenic from Low Concentration of Formic Acid Media

A highly sensitive method for the determination of total\narsenic\n(As) has been developed using photochemical vapor generation (PVG)\ncoupled with inductively coupled plasma mass spectrometry (ICP MS).\nThe efficient PVG of As is reported for the first time in the presence\nof Cd(II) in diluted formic acid (FA) medium. The PVG efficiency of\n93 ± 1% can be achieved in the system with 0.15% (v/v) FA and\n40.0 mg L<sup>–1</sup> Cd(II) under 100 s UV irradiation. The\nlimit of detection (LOD, 3σ) for As was determined to be 0.2\nng L<sup>–1</sup>, which was enhanced about 43-fold over the\ntraditional solution nebulization method. The anti-interference capability\nagainst sample matrices was enhanced compared to previous PVG systems\nthat used diluted formic acid alone or a combination of sodium formate\nand sodium sulfite as the medium. The established method was applied\nfor the analysis of natural waters and certified reference materials\n(CRMs) of rice with satisfactory results. The mechanism of the PVG\nsystem was investigated, and the generation of volatile As species\nas AsH<sub>3</sub> was found in all investigated systems, including\nmonomethylarsonic acid (MMA), dimethylarsinic acid (DMA), As (III),\nand As(V). Additionally, volatile cadmium species were also generated\nsimultaneously. The efficient reduction of As in diluted FA observed\nin this study is beneficial to understanding the interaction between\nAs and Cd in the photochemical process.