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.