Ultrasonication-assisted spray ionization

The predecessor of PI-ESI was ultrasonication-assisted spray ionization (UASI) [107, 108]. In that early version, one end of a sample capillary was dipped in the sample vial held in an ultrasonicator (frequency 40 kHz) while the other (tapered) end was placed close ( 3 mm) to the MS inlet. Although no electric potential was applied to the tapered end of the capillary, electrospray could be observed, and mass spectra of analytes with... 

Chen, T.-Y, Chao, C.-S., Mong, K.-K.T, Chen, Y.-C. (2010)Ultrasonication -assisted Spray Ionization Mass Spectrometry for On-line Monitoring of Organic Reactions. Chem. Commun. 46 8347-8349. 

Lin, S.-H., Lo, T.-J., Kuo, F.-Y, Chen, Y.-C. (2014) Real Time Monitoring of Accelerated Chemical Reactions by Ultrasonication-assisted Spray Ionization Mass Spee-trometry. J. Mass Spectrom. 49 50-56. 

Contrary to V-EASI, in the case of polarization induced (PI)-ESI [e.g., contactless atmospheric pressure ionization (C-API) and ultrasonication-assisted spray ionization (UASl)] [39-41], one does not need to supply nebulizing gas, which makes the monitoring system even more simplistic. In C-API, a glass capillary ( 20 cm, inner diameter 50 pm) was inserted to the reaction vial to direct the reaction solution toward the mass spectrometer. The tapered end of this capillary was placed in proximity ( 1 mm) to the inlet of the mass spectrometer (Figure 11.2a). The flow of sample was mainly due to capillary action and the influence of the electric field near the mass spectrometer, which may induce some electroosmotic flow (EOF) (see Chapter 6). In this approach, the sample flow rate is low ( 100 nl min" ). The sampling time can be reduced by using a shorter capillary as the sampling tube. Similarly to V-EASI, the capillary combines... 

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