| Abstract
| - The different spraying modes in electrospray ionizationsources exhibit large variations in their ion yield andstability. To achieve consistently optimal ion production,active control of the spray parameters is desirable. Todiagnose the changes in spraying mode, the spray currentand its Fourier spectrum were monitored under a widerange of conditions, that is, as a function of the sprayvoltage, liquid flow rate, and composition. Most Fourierspectra indicated a strong dc component, a low-frequencybranch at low flow rates and applied voltages, and a high-frequency branch and their harmonics. Changing of theseparameters resulted in several spraying mode changesthat were reflected in the Fourier spectra of the spraycurrent. Significant mode changes and the malformationof the Taylor cone were detected as peak shifts or suddenchanges in the spectrum quality. This was confirmed byfast imaging that showed a reduction in the size of theTaylor cone under hydrophobic tip conditions and rapidperiodic ejection of filaments and droplets for high conductivity solutions. Comparing the oscillation frequenciesof Taylor cones of different sizes, good correlation wasfound with the frequencies of capillary waves on comparablly sized liquid spheres. Spray stability was also linkedwith the positional stability of the contact line between theliquid meniscus and the capillary tip.
|
