Asymmetrical Emitter Geometries for Increased Range of Stable Electrospray Flow Rates

Because electric field distribution is determined by emitter size and shape, sprayer tip geometry determines the optimum liquid flow rate that can be processed by the electrospray ionization interface. Electric field is the highest at the sharpest edge of an electrode; therefore, for a beveled tip, the field is highest at the very tip, and for a conventional symmetrically tapered tip, the field is the highest around the rim of the electrode. Electrospray performance as a function of flow rate was investigated using both continuous infusion and peak-based analysis. The sharpest symmetrical emitter gave the most stable electrospray ionization (ESI) at flow rates <= 0.10 mu L/min, while beveled emitters provided significantly better performance at expanded flow rates up to 1 mu L/min. The use of beveled emitters offers the potential for increased versatility in electrospray ionization interfaces.