Naturally and externally pulsed electrospray

The current studies on pulsation phenomena in electrospray ionization, and pulsed electrospray ionization (ESI) under external electrical control are reviewed. A number of investigations have shown that two types of pulsation processes exist: low-frequency fluctuation and high-frequency droplet-formation. The low-frequency pulsation is induced by an imbalance between the flow rate of the input sample to the Taylor cone and the feed rate of the output solution to the liquid filament. The high-frequency pulsation mainly results from the initial droplet formation process, and is modulated by the low-frequency pulsation. The fundamental and experimental sections of these two pulsations are discussed. Experimental results also show that low and high pulsations can both be controlled electrically to create a pulsed ESI so that high sensitivity and an enhanced S/N ratio can be achieved. However, the co-ordination of the synchronization between a natural pulsation and a pulsed ESI, as well as its application to mass spectrometer (MS) analysis, demands further research.