Ambient Ion Soft Landing

Abstract

Ambient ion soft landing, a process in which polyatomic ions are deposited from air onto a surface at a specified location under atmospheric pressure, is described. Ions generated by electrospray ionization are passed pneumatically through a heated metal drying tube, their ion polarity is selected using ion deflectors, and the dry selected ions are soft-landed onto a selected surface. Unlike the corresponding vacuum soft-landing experiment, where ions are mass-selected and soft-landed within a mass spectrometer, here the ions to be deposited are selected through the choice of a compound that gives predominantly one ionic species upon ambient ionization; no mass analysis is performed during the soft landing experiment. The desired dry ions, after electrical separation from neutrals and counterions, are deposited on a surface. Characterization of the landed material was achieved by dissolution and analysis using mass spectrometry or spectrofluorimetry. The treated surface was also characterized using fluorescence microscopy, which allowed surfaces patterned with fluorescent compounds to be imaged. The pure dry ions were used as reagents in heterogeneous ion/surface reactions including the reaction of pyrylium cations with d-lysine to form the N-substituted pyridinium cation. The charged microdroplets associated with incompletely dried ions could be selected for soft landing or surface reaction by choice of the temperature of a drying tube inserted between the ion source and the electrical ion deflectors.

Reactions of Microsolvated Organic Compounds at Ambient Surfaces: Droplet Velocity, Charge State, and Solvent Effects

“…The middle electrode is a 5 mm thick (5×5 cm square) stainless steel with a circular hole (1 cm in diameter) at its center. It allows ions to be focused onto the collector/reaction surface [39]. The typical diameter of the ion spot observed under this condition was 2 mm, but actual spot size depended not only on the thickness of the middle electrode but also on the magnitude of the DC potentials applied [39].…”

“…It allows ions to be focused onto the collector/reaction surface [39]. The typical diameter of the ion spot observed under this condition was 2 mm, but actual spot size depended not only on the thickness of the middle electrode but also on the magnitude of the DC potentials applied [39]. Sample solutions of 50-2000 ppm concentration were prepared in methanol or acetonitrile.…”

“…For surface reactions, the selected ion is given enough energy to react selectively with particular functional groups present at the surface. Recently, the SL technique was extended from vacuum to ambient conditions in a process termed ambient soft landing [39]. In ambient ion soft landing, polyatomic organic ions are deposited from air onto a surface at a specified location under atmospheric pressure conditions.…”

“…The advantage of this type of electrospray (ESI [29,42,43]) is that it allows some solvent evaporation from the droplets during their transfer to the designated location, and the use of the derived charged microdroplets for surface reactions at atmospheric pressure. To effect surface reaction, the charged microdroplets containing the desired reagent ion were directed onto the reaction surface containing a nominally dry reagent using the ambient soft landing apparatus [39,44]. Under particular experimental conditions (discussed later), this apparatus allows focusing of the ions onto a 2 mm (diameter) spot size, producing no observable macroscopic solvent on the surface.…”

Accelerated C–N Bond Formation in Dropcast Thin Films on Ambient Surfaces

“…Solvent evaporation leading to rate enhancement of chemical reactions has recently been reported for charged microdroplets reactor systems generated in reactive desorption electrospray ionization (DESI) [1,10,11] and ambient ion soft landing [12][13][14] experiments. Traditionally, the advantages of microreactor systems are recognized to include rapid mixing of reagents, effective control of reaction time, and the ability to control interfacial chemistry [15].…”