Mechanistic studies on the trapping and desorption of volatile hydrides and mercury for their determination by electrothermal vaporization-inductively-coupled plasma mass spectrometry

Metallic coatings in the pyrolytic graphite furnace have been used for the pre-concentration of Hg (using electrochemically reduced Au) and AsH3 (using both thermally and electrochemically reduced Ir and Pd/Ir) prior to electrothermal volatilization. The analyte trapping efficiency during accumulation and the analyte and modifier release processes during volatilization were monitored in real time. This was achieved by using the fast response capability of inductively-coupled plasma-mass spectrometry to determine simultaneously both the analyte and modifier elements as a function of time. The temperature dependence of the analyte trapping process points to contrasting mechanisms for Hg adsorption on Au (reversible, physical adsorption/amalgamation) and for AsH3 adsorption on Pd, Ir or Pd/Ir (physical adsorption followed by an irreversible hydrogen abstraction reaction at active sites). Results also indicate that only minor volatilization of modifier occurs at the temperature required for volatilization of analyte from the furnace.