Nozzle and liquid effects on the spray modes in nanoelectrospray

Unforced nanoelectrospray can exhibit a number of stable spray modes. These include low frequency pulsations, high frequency pulsations, and a steady cone-jet. Experiments are reported here on such pulsations that have been observed in various salt loaded solutions of ethylene glycol, triethylene glycol and water. The spray current was monitored with I mu s time resolution to show that spray regime characteristics depend on nozzle diameter and liquid conductivity. The frequency of pulsations was found to increase with both increased liquid conductivity and decreasing nozzle diameter. The charge ejected during a pulse is lower for smaller nozzles spraying higher conductivity liquids. Water solutions were observed undergoing high frequency pulsations, with these pulsations often occurring in lower frequency bursts. The frequencies of water pulsations were as high as 635 kHz but the charge ejected by each pulsation was an order of magnitude lower than that observed in triethylene glycol. An unforced electrospray of water was also identified as being in the steady cone-jet mode with a higher degree of confidence than previously. The values for stable pulsation frequency and charge ejected observed in ethylene glycol lay between those of TEG and water. (c) 2006 Elsevier Inc. All rights reserved.