Efficient analyte oxidation in an electrospray ion source using a porous flow-through electrode emitter

Abstract

This article describes the components, operation, and use of a porous flow-through electrode emitter in an electrospray ion source. This emitter electrode geometry provided enhanced mass transport to the electrode surface to exploit the inherent electrochemistry of the electrospray process for efficient analyte oxidation at flow rates up to 800 L/min. An upstream current loop in the electrospray source circuit, formed by a grounded contact to solution upstream of the emitter electrode, was utilized to increase the magnitude of the total current at the emitter electrode to overcome current limits to efficient oxidation. The resistance in this upstream current loop was altered to control the current and "dial-in" the extent of analyte oxidation, and thus, the abundance and nature of the oxidized analyte ions observed in the mass spectrum. The oxidation of reserpine to form a variety of products by multiple electron transfer reactions and oxidation of the ferroceneboronate derivative of pinacol to form the ES active radical cation were used to study and to illustrate the performance of this new emitter electrode design. Flow injection, continuous infusion, and on-line HPLC experiments were performed. (J Am Soc Mass Spectrom 2004, 15, 1755-1766

Using the Electrochemistry of the Electrospray Ion Source

“…Only when the current was limited to that measured in an actual ES MS experiment (6 µA) did the efficiency drop below 100%, and then only at flow rates >500 µL/ min. These calculated results are in agreement with the published experimental data (14). Averaged ES mass spectra were acquired at the plateau region of a large-volume injection of a 20-µM solution of reserpine (Scheme 2 in Supporting Information) at a flow rate of 50 µL/min with a platinum capillary or porous flow-through electrode emitter.…”

Perspective on Electrospray Ionization and Its Relation to Electrochemistry

“…The Van Berkel group, among many other contributions to the electrochemistry/electrospray field [76][77][78][114][115][116][117][118][119][120], attempted a full-scale numerical simulation of current and potential distribution in the electrospray capillary [121]. The project was based on solving the Laplace equation with boundary conditions corresponding to the actual geometric and flow conditions in the electrospray capillary.…”

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

“…Comparison of I W values in Tables 2, and the corresponding reserpine oxidation efficiencies apparent in the spectra in Figure 3b reveals again that the magnitude and polarity of I W defines the reserpine oxidation efficiency, even if R BAT is changed. R BAT has an important effect by defining I BAT in this extra circuit as I TOT is practically defined by the solution composition, [6,10,11] I BAT defines the current window within which I W can be changed. This observation is well demonstrated by the Ϫ1.8 to ϩ5.3 A and Ϫ3.3 to ϩ2.9 A ranges for I W accessible using R BAT ϭ 4.26 and 2.06 M⍀, respectively (Tables 1 and 2).…”

“…[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.…”

“…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.…”