Direct detection of solid inorganic mercury salts at ambient pressure by electron-capture and reaction-assisted HePI mass spectrometry

Solid HgCl₂ is readily detected at ambient conditions by electron capture in a HePI-MS source. The captured electron occupies the empty 6 s orbital of the Hg atom. The resulting radical-anion HgCl₂ ^-• can exist as three "flexomers" of different Cl-Hg-Cl angle. The facile in-source formation of HgCl₂ ^-• and the adduct [HgCl₃]^- is exploited to detect other solid Hg compounds by exposing them to an external chloride source, such as HCl, NaCl, or vapors emanating from solid TiCl₃. In situ oxidation of Hg₂Cl₂ with H₂O₂ generated signals for HgCl₂ ^-• and [HgCl₃] ^-, suggesting that oxidation makes Hg 6 s orbital available for electron capture.