We examine our earlier finding that AC electrospray cone can preferentially entrain and concentrate low-mobility ions generated at the cone tip [Chetwani, Maheshwari and Chang, Phys Rev Lett., 101, 204501 (2008)]. Instead of tip ionization, we scrutinize entrainment effects on dispersed ionic species in the spray solution. Fluorescence images of ejected ionic species, including anionic oxide ions, organic dyes, charged nano-particles, and stained DNA from AC electrospray cone generated with a 4–5 kV source. Negatively charged species such as anionic dyes concentrate at the tip of AC spray cone before ejection. Cationic dyes are more homogeneously distributed in the cone during ejection. Larger particles with negative charges, including fluorescence dye-tagged nano-particles (about 50 nm) and dye-stained DNA, have similar spatio-temporal evolutions of anioic dyes within the cone before ejection. These observations extend our previous entrainment and concentration effect to AC spray without ionization. The images will be correlated with tandem Mass Spectrometry and will be used to selectively gate either cationic (protein) or anionic polymers (DNA).

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