Atomic and molecular spectra of vapors evolved in graphite furnace. Part 6: Sulfur

Abstract

The vaporization of micrograms of sulfur, sulfuric acid, Cu, Hg, Ni and Zn sulfides and Ca sulfate in graphite electrothermal vaporizers (ETV) for atomic absorption spectrometry is investigated using UV spectrometer with charge-coupled device (CCD) detector and deuterium light source. Fifty vapor absorption spectra (187–380 nm) are acquired during 10-s temperature ramp of the ETV from 500 to 2300 K or from 700 to 2700 K. The spectral patterns reflect vapor evolution and composition during the vaporization pulse. A pyrocoated graphite tube is used as ETV, and a filter furnace is also employed to highlight spectral patterns that indicate the interaction of sample vapor with graphite. The vapor spectra having similar features and, therefore, characteristic for common vapor components are discussed. Two types of spectra between 240 and 320 nm are attributed to S 2 (structured spectrum) and SO/SO 2/SO 3 (diffuse spectrum) species according to their behavior in the tube and filter furnace. The spectrum observed at 250–270 nm correlates with that of CS. It is also observed that sulfur and all sulfur compounds except HgS induce structured spectra approximately 200 nm if an excess of carbon in contact with sulfur vapor is provided. It is suggested that the spectrum belongs to molecule C n S m (with n> m), formed in sample vapor if experimental conditions are favorable. Diffuse bands at 187–230 nm precede or accompany the appearance of molecular spectra. Light scattering by molecular clusters is suggested to explain the phenomenon.