Atomic and molecular spectra of vapors evolved in a graphite furnace. Part 4: alkaline earth chlorides

Dry residues of aqueous solutions of alkaline earth chlorides (100 μg as element) were vaporized in the Ta-lined and pyrocoated graphite furnace during temperature ramp from 400° to 2400–2500°C. Absorption and emission spectra were obtained in the 200–475 nm range using a dedicated CCD spectrometer. BeCl2 in aqueous solutions showed an almost complete hydrolysis prior to the vaporization. The spectra were characterized by the contemporaneous presence of intense light scattering and emission continuum, in analogy with the behavior of Be(NO3)2 already examined. By applying BeCl2 slurry in chloroform enabled the observation of BeCl2 and BeCl species in the vapor phase. Aqueous solution of MgCl2 showed the evolution of di-halide species at low temperatures and the vaporization pattern with the emission continuum and light scattering similar to that observed for Mg(NO3)2 at higher temperature. The hydrolysis of the di-chlorides decreases for the alkaline earth elements with increasing of atomic mass. The Ca, Sr and Ba chlorides showed a vaporization pattern of di-chloride in both a pyrocoated and Ta-lined tube with increased simultaneous appearance of mono-chloride and atomic species in the pyrocoated tube. The proposed explanation indicates a trend to the decomposition due to the sample vapor interaction with graphite.