Hydrogen Sulfide Detection by UV-Assisted Infrared Spectrometry

Abstract

Ultraviolet (UV)-assisted infrared (IR) spectroscopy has been evaluated for its potential usage and feasibility to indirectly detect hydrogen sulfide gas. Hydrogen sulfide (H2S) is a weakly IR-absorbing compound, and its detection by IR methods is further complicated by severe water interferences. However, H2S can readily be converted to sulfur dioxide (SO2), a strong IR absorber, via ultraviolet irradiation. A multipass IR White cell equipped with an internal mercury germicidal UV lamp has been interfaced to a Bomem MB series Fourier transform infrared (FT-IR) spectrometer. The conversion of hydrogen sulfide to sulfur dioxide (SO2) was tested in five matrices: nitrogen, ambient air, moisturized ambient air, dried ambient air, and zero-grade air. The conversion efficiency of H2S to SO2 in nitrogen, containing a negligible amount of oxygen, was approximately 25% and peaked at approximately 6 min of UV irradiation. In ambient air, the conversion efficiency was calculated to be ∼45% and peaked at 35 s of irradiation, while in the dried ambient air the SO2 concentration peaked in 85 s. In ambient air, the generated SO2 was destroyed during its production and was below detection within 90 s of irradiation. In the dried ambient air, the generated SO2 was still detectable at 120 s of irradiation. Moisturized ambient air was investigated to determine the degree of SO2 loss due to reaction with H2O. From these data, it appears that the water molecule and SO2 photolysis contribute only slightly to the SO2 loss. The greatest loss is apparently caused by reactive radicals such as ·OH generated during UV irradiation. Index Headings: FT-IR; UV photolysis; Vapor phase; H2S; SO2; Environmental analysis.