Expanded use of a battery-powered two-electrode emitter cell for electrospray mass spectrometry

Journal of The American Society for Mass Spectrometry, Jul 2006

A battery-powered, controlled-current, two-electrode electrochemical cell containing a porous flow-through working electrode with high surface area and multiple auxiliary electrodes with small total surface area was incorporated into the electrospray emitter circuit to control the electrochemical reactions of analytes in the electrospray emitter. This cell system provided the ability to control the extent of analyte oxidation in positive ion mode in the electrospray emitter by simply setting the magnitude and polarity of the current at the working electrode. In addition, this cell provided the ability to effectively reduce analytes in positive ion mode and oxidize analytes in negative ion mode. The small size, economics, and ease of use of such a battery-powered controlled-current emitter cell was demonstrated by powering a single resistor and switch circuit with a small-size, 3 V watch battery, all of which might be incorporated on the emitter cell.

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Expanded use of a battery-powered two-electrode emitter cell for electrospray mass spectrometry

Vilmos Kertesz 0 1 Gary J. Van Berkel 0 1 0 Published online May 12, 2006 Address reprint requests to Dr. V. Kertesz, Organic and Biological Mass Spectrometry Group, Chemical Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831-6131, USA 1 Organic and Biological Mass Spectrometry Group, Chemical Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee, USA A battery-powered, controlled-current, two-electrode electrochemical cell containing a porous flow-through working electrode with high surface area and multiple auxiliary electrodes with small total surface area was incorporated into the electrospray emitter circuit to control the electrochemical reactions of analytes in the electrospray emitter. This cell system provided the ability to control the extent of analyte oxidation in positive ion mode in the electrospray emitter by simply setting the magnitude and polarity of the current at the working electrode. In addition, this cell provided the ability to effectively reduce analytes in positive ion mode and oxidize analytes in negative ion mode. The small size, economics, and ease of use of such a battery-powered controlled-current emitter cell was demonstrated by powering a single resistor and switch circuit with a small-size, 3 V watch battery, all of which might be incorporated on the emitter cell. (J Am Soc Mass Spectrom 2006, 17, 953-961) 2006 American Society for Mass Spectrometry - Eoperation of an electrospray ion source as typilectrochemistry is an inherent part of the normal cally configured for electrospray mass spectrometry (ES-MS) [1, 2]. Oxidation reactions in positive ion mode and reduction reactions in negative ion mode are the predominate reactions at the emitter electrode contact (i.e., the working electrode in this system) that supply the excess of one ion polarity in solution required to maintain the quasi-continuous production of unipolar charged droplets and subsequently gas-phase ions. Our interest in this electrochemical process is aimed towards better understanding the process to devise means to control it for analytical advantage. The electrochemical reactions at the emitter electrode alter the composition of the solution being electrosprayed, and they can also directly involve the analytes being investigated. Thus, under certain conditions, with particular types of analytes, the electrochemical reactions in the ES ion source can have a significant influence on the identity and abundance of ions observed in an ES mass spectrum [1, 3, 4]. In particular, we have been interested in controlling direct heterogeneous electron-transfer chemistry of the analytes under study and their potential homogeneous chemical follow up reactions. Basic principles of electrochemistry dictate [5] and ES-MS experimentation and calculation [3] have shown that varied degrees of control over the electrochemical processes involving the analytes can be achieved by managing one or more of three basic parameters, viz., mass transport to the ES emitter electrode, the magnitude of the current (more precisely, current density) at the ES emitter electrode, and the ES emitter electrode potential. In our most recent research efforts, we have developed a porous flow-through (PFT) electrode emitter [6, 7], replacing the standard capillary electrode emitter, to provide very efficient mass transport of analytes in solution to the electrode even at flow rates approaching 1 mL/min. With this emitter electrode design all of the analyte in solution will contact the surface of the PFT electrode on passage through the emitter and very efficient oxidation or reduction of analytes can be achieved as long as the reactions are not current limited, limited by the interfacial electrode potential, or limited by other reaction rate considerations. A PFT electrode emitter enhances the ability to directly involve the analytes under study in the electrochemistry of the ES process. However, one would like to use this basic electrode configuration as a general ES emitter so that it need not be replaced for experiments in which analyte electrochemistry is not of interest or is to be avoided. Control over which reactions can take place at the emitter electrode, and the rate at which they take place, is achieved by controlling the interfacial potential of the electrode. This can be accomplished to some degree with a single electrode system by limiting the magnitude of the current at the emitter electrode through adjustable parameters like solution conductivity or ES voltage drop. Lower current magnitudes either current limit the reaction (Faradays law) or lower the current density at the electrode so that the potential at the electrode drops to a level lower than that required for the analyte reaction (but still sufficient for another reaction, e.g., solvent electrochemistry, to provide the required current). Another means to control the potential with a single electrode emitter is through the (...truncated)


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Vilmos Kertesz, Gary J. Van Berkel. Expanded use of a battery-powered two-electrode emitter cell for electrospray mass spectrometry, Journal of The American Society for Mass Spectrometry, 2006, pp. 953-961, Volume 17, Issue 7, DOI: 10.1016/j.jasms.2006.02.007