Characterization of water-ethanol electrosprays

The electrospray (ES) ionization method is widely used in the analysis of biological molecules. The stable cone regime spray is usually obtained by adding methanol or ethanol to the electrosprayed dipolar fluid, with the role of reducing fluid surface tension. We investigate the spray onset voltages of water-ethanol mixtures starting from distilled water to pure ethanol. Positive or negative DC is applied separately in our measurements. The experimental setup allows for the study of nozzle-counter electrode gaps of up to 50 cm. Significant variations in the spray onset are observed and analyzed. The onset voltage and the surface tension of water-ethanol binary mixtures appear to be in line with Smith's formula. The largest variations of onset values are observed for surface tensions of 20 mN/m-40 mN/m in the mixtures. The results of the study may be instrumental to electrospray electrode design and spray control. (C) 2011 Published by Elsevier B.V.