Spray current

Polymeric microfluidic systems coupled to a microfabricated planar polymer tip can be used as a stable ion source for ESI-MS. A parylene tip at the end of the microchannel delivers fluid which easily produces a stable Taylor cone at the tip via an applied voltage. The described device appears to facilitate the formation of a stable spray current for the electrospray process and hence offers an attractive alternative to previously reported electrospray emitters. When this interface was employed for the quantification of methylphenidate in urine extracts via direct infusion MS analysis, this system demonstrated stable electrospray performance, good reproducibility, a wide linear dynamic range, a relatively low limit of quantification, good precision and accuracy, and negligible system carryover. We believe polymeric devices such as described in this report merit further investigation for chip-based sample analysis employing electrospray MS in the future. 

Yushchenko, K., Borisov, Y., Pereverzev, Y., Balakin, V., and Smith, R. (1995) Thermal Spraying-Current Status and Future Trends, ASM International, vol. 1, Proceedings of ITSC 95, Kobe, Japan, 1995, pp. 273-274. 

P.J. Meyer, Economics ofMCrAlY coatings, in Thermal Spraying Current Status and Future Trends, Proceedings of the 10th International Thermal Spray Conference, Kobe, Japan, 2004, 2004, pp. 217-222. 

Spray Current, Droplet Radius and Droplet Charge... 

The minimum ion concentration for an electrospray has been experimentally determined as 10 mol [9]. When this minimum concentration is met, on the basis of theoretical reasoning and experimental measurements [10], the following relationships for spray current I, drop radius R and droplet charge q have been proposed ... 

Fig. 2 MS signal (black) for a 10 )iM reserpine solution (50 % methanol in water with 0.1% acetic acid) as a function of the applied voltage/ electrospray operating regime (Adapted with permission from Ref. [5], copyright American Chemical Society), (b) MS signal (black) and spray current (cyan) for a 5 pM leucine enkephalin solution (33 % acetonitrile in water with 1 % trifluoroacetic acid) as a function of applied voltage (Adapted with permission from Ref. [6], copyright American Chemical Society)...

A preliminary survey has been carried out to see whether Mexican fruit fly infestation present along the Califomia-Mexico border can be controlled by the sustained release of sterile flies. It was thought that this would be more economic than the present method of quarantine survey and insecticide spraying currently costing approximately 100,000/year. 

The cone-jet mode at the spray capillary tip described and illustrated in Figures 1.1 and 1.3a is only one of the many possible ES modes. For a qualitative description of this and other modes, see Cloupeau [13a-c]. More recent studies by Vertes and coworkers [15] using fast time-lapse imaging of the Taylor cone provide details on the evolution of the Taylor cone into a cone jet and pulsations of the jet. These pulsations lead to spray current oscillations. The current oscillations are easy to determine with conventional equipment and can be used as a guide for finding conditions that stabilize the jet and improve signal-to-noise ratios of the mass spectra. The cone-jet mode is the most used and best characterized mode in the electrospray literature [12, 13]. 

For experiments with controlled spaying mode, stainless steel electrode with oscilloscope to perform spray current measurements (e.g., WaveSurfer 452, LeCroy, Chestnut Ridge, NY, USA). 

While sampling intact sample areas, optimize the spray voltage for LAESI ion yield. (Optional) Follow the temporal behavior of the spray current on a counter electrode with an oscilloscope to determine the flow rate and spray voltage conditions for the cone-jet spraying mode (see Notes 4.3.1... 

Stability of charged droplet generation with the electrospray source is critical for successful ion production with the LAESI source. Sudden changes in the ion or spray current levels usually point to unstable liquid dispersion. Inspect connections and look for material deposition and oxidation on the emitter tip. Clean the emitter tip with the electrospray solvent. Alternatively, replace emitter if required. 

Herman, H., Sampath, S. and McGune, R. (2000), Thermal spray current status and future trends, MRS Bulletin 25, 17-25. 

To stabilize the spray current and prevent unwanted chemical noise, it is desirable to take steps to eliminate corona discharge. Corona discharge can be suppressed by the use of chlorinated solvents or electron scavenging sheath gases such as O2 or Another... 

Figure 3.13. Diagram of the electrical circuit for a controUed-potential electrochemistry-ES emitter. Floated potentiostat common is that of the ES high-voltage supply. W, R, and A represent the working, reference, and auxiUary electrodes in the electrochemical ceU, respectively, /w, Aux, fe, ext are the currents in the working electrode, auxiUary electrode, ES spray current, and upstream external current loop, respectively. In standby mode the electrodes remain connected to the ES high voltage, but the worki ng electrode potential is not controlled with the potentiostat. (Adapted with permission from Ref. 89. Copyright 2005, American Chemical Society.)...

Y. Fukuda and M. Kumon, Thermal Spraying, Current status and future trends, ed. A. Ohmori, High Temperature Society of Japan, Osaka, Japan, 1995, 107. 

---