Efficient Photochemical Generation of Germanium and Arsenic Hydrides in a Sulfite and Iodide Medium

In this study, highly efficient photochemical vapor generation (PVG) of germanium (Ge) and arsenic (As) in the absence of organic compounds was first reported. Volatile As and Ge species were formed in the system containing sulfite and iodide under UV irradiation. In a medium containing 12 mM Na₂SO₃ and 90 mM KI, the PVG efficiency was 88 ± 1% for Ge after 80 s of UV irradiation, with the limit of detection (LOD, 3σ) of 0.2 ng L^-1 by ICP MS measurement. Under the conditions of 2 mM Na₂SO₃, 200 mM KI, and 10 s of UV irradiation, the PVG efficiency was 43 ± 1% for As with the LOD of 0.6 ng L^-1. Moreover, the analytical sensitivities for As(III) and As(V) were comparable, making it possible to directly determine total As. The developed method was applied for the analysis of Ge and As in soil and water samples with satisfactory results. The mechanism for the photochemical reduction of Ge and As was explored in this study by gas chromatography-mass spectrometry (GC-MS) and electron paramagnetic resonance. It was found that the volatile species of Ge and As generated during the photochemical reaction were GeH₄ and AsH₃, respectively. The synergistic effect from sulfite and iodide promoted the continuous and stable generation of e_aq^- and increased the synthesis of ^•H under UV irradiation as well. The finding is significant for the understanding the photochemical conversion of Ge and As in the system without organic acids.