Characterization of bis(alkylamine)mercury cations from mercury nitrate surfaces by using an ion trap secondary ion mass spectrometer

Mercury-cyclohexylamine (R-NH₂, where R = c-C₆H₁₁) ions having the composition Hg(R-NH)₂H⁺ can be formed by exposing the surface of Hg(NO₃)_n=1,2 salts to gaseous primary amines and then sputtering the surface with a primary ion beam (ReO^-₄). The resultant ions can be stabilized and detected using an ion trap secondary ion mass spectrometer (IT-SIMS) instrument, which provides collisional stabilization that facilitates their observation. Isolation of the Hg(R-NH)₂H⁺ ions followed by collisional activation produces daughter ions corresponding to (C₆H₁₀NH₂)⁺and Hg(R-NH)⁺. These assignments were supported by deuterium labeling experiments, which resulted in the formation of Hg(R-NH)(R-NH-d₁₁)H⁺ and Hg(R-NH)₂H⁺. The existence of the Hg(R-NH)₂ compounds on the surface was verified using Raman spectroscopy, which showed a strong absorption at 590 cm^-1 that corresponded to Hg-N stretching. Analogous ions could be formed with n-hexylamine, but no Hg-bearing ions were formed when starting with a secondary or a tertiary amine. This indicates that only primary amines will react with Hg-nitrate surfaces in this manner. Hg-amine ions could not be formed starting with other Hg salts: chloride, iodide, thiocyanate, sulfate, and oxide. These results suggest that surface derivatization using amines, coupled with an IT-SIMS instrument, may offer an approach for determining inorganic metal speciation on surfaces. (J Am Soc Mass Spectrom 1998, 9, 35-41)