Measurement of Parts per Million Level Gaseous Concentration of Hydrogen Sulfide by Ultraviolet Spectroscopy using 1,1,1,5,5,5-Hexafluoropentan-2,4-dione as a Derivative by Reaction of Cu(hfac)(1,5-Cyclooctadiene)

Hydrogen sulfide reacts rapidly and quantitatively at ppm levels with cycloocta-1,5-diene-1,1,1,5,5,5-hexafluoropentan-2,4-dionatocopper(I) (Cu(hfac)(COD)) to yield 1,1,1,5,5,5-hexafluoropentan-2,4-dione (Hhfac) having a strong ultraviolet absorption at 268 nm, and which can be used without interference as a derivative in the continuous, fast online spectroscopic determination of the H₂S concentration. The analytical method has excellent selectivity and can be used in the presence of N₂, H₂, CO, COS, SO₂, moist air, CH₃OH, C₂H₄, C₆H₆, and light alkanes including fuel gases. Using a standard spectrometer, the level of detection is about 10 ppb. Concentrations down to 1 ppm H₂S can be analyzed readily, usually with an error in the range 0 to −7% dependent largely on the sorption characteristics of the apparatus. These are systematic errors due to adsorption; however, the analytical apparatus was very stable, and relative standard deviations as low as 0.1% of the mean can be obtained. The method can also be applied to the analysis of methanethiol.