Hydrogen Sulfide Detection by UV-Assisted Infrared Spectrometry

Ultraviolet (UV)-assisted infrared (IR) spectroscopy has been evaluated for its potential usage and feasibility to indirectly detect hydrogen sulfide gas. Hydrogen sulfide (H 2 S) is a weakly IR-absorbing compound, and its detection by IR methods is further complicated by severe water interferences. However, H 2 S can readily be converted to sulfur dioxide (SO 2 ), 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 (SO 2 ) was tested in five matrices: nitrogen, ambient air, moisturized ambient air, dried ambient air, and zero-grade air. The conversion efficiency of H 2 S to SO 2 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 SO 2 concentration peaked in 85 s. In ambient air, the generated SO 2 was destroyed during its production and was below detection within 90 s of irradiation. In the dried ambient air, the generated SO 2 was still detectable at 120 s of irradiation. Moisturized ambient air was investigated to determine the degree of SO 2 loss due to reaction with H 2 O. From these data, it appears that the water molecule and SO 2 photolysis contribute only slightly to the SO 2 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; H 2 S; SO 2 ; Environmental analysis.