Can one observe "atomic absorption" in solution pase?

Abstract

Atomic absorption spectrometry in aqueous phase has been tried with 0.03M K₂SO₄ and 1% H₂SO₄ solutions of Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Hg²⁺, Hg₂²⁺, Tl⁺, Ag⁺ and Pb²⁺. As means of atomization, electrolysis and chemical reduction were employed. In the case of electrolytic reduction, the spectral change was examined in situ using platinum minigrids as optically transparent electrodes or the platinum plate which was set parallel to the incident light beam. A spectrum with an intensive peak at 238nm was observed when the Hg²⁺ solution was electrolyzed. This absorption peak did not decrease even if the applied potential was cut off, and is identified as the spectrum of Hg₂²⁺ ions which was formed by: Hg²⁺+e=1/2Hg₂²⁺ and/or Hg²⁺+Hg⁰=Hg₂²⁺. The peak at 231 nm was also obtained with Cd²⁺ solution by electrolysis, which may be ascribed to Cd⁺. Furthermore, Tl⁺, Ag⁺ and Cu²⁺ gave broad absorption peaks at 240, (245, 310), and 277 nm, respectively. On the contrary, Mn²⁺, Co²⁺, Ni²⁺, Zn²⁺ and Pb²⁺ gave no significant change in spectra although the applied potential went up to -2.5 V. The absorption peak at 207 nm obtained by electrolysis of Zn(II) solution, which is reported by Tyson and West, was found to be identical to that of Zn(II) in excess NaOH, suggesting that this is due to the Zn(II)-hydroxo complex rather than Zn(0) species. A new doublet spectrum which has peaks at 251 and 257 nm was found immediately after adding reducing reagent, SnCl₂, to Hg₂²⁺ or Hg²⁺ solution. This absorption decayed in 3min, and was not ascribed to SnCl₂, SnCl₄, or H₂SO₄ in aqueous solution. Therefore, it appears that the observed spectrum is responsible for the "atomic absorption" of hydrated mercury.