Electrospraying Large Sparingly Soluble Tetraalkylammonium Ions as Monomobile Standards of Moderately Low Electrical Mobility

Abstract

A procedure is described to electrospray the relatively large ions tetrahexadecylammonium (C16H33)4N+ and tetraoctadecylammonium (C18H37)4N+ from their commercially available bromide salts. Their low solubility and the corresponding low conductivity of their alcohol solutions complicates their electrospraying by the convenient method of applying the high voltage to the solution reservoir (rather than to the electrospraying tip). If the capillary bore is widened to reduce the reservoir-tip electrical resistance, the solvent evaporates at its tip, leading to solute precipitation and spray destabilization. These difficulties are overcome via conventional nanospray: we use a wide (∼100 μm ID) capillary whose tip is pulled in a flame down to <20 μm OD. Mobility spectra result where the dominant and most mobile peaks are (C16H33)4N+ or (C18H37)4N+. Their electrical mobilities in air at room temperature and pressure are 0.63 and 0.60 cm2/V/s (±1%).Copyright 2015 American Association for Aerosol Research