Computational Simulation of Redox Reactions within a Metal Electrospray Emitter
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- 作者：Gary J. Van Berkel ; Gary E. Giles ; Jonathan S. Bullock ; IV ; and Leonard J. Gray
- 刊名：Analytical Chemistry
- 出版年：1999
- 出版时间：December 1, 1999
- 年：1999
- 卷：71
- 期：23
- 页码：5288 - 5296
- 全文大小：141K
- 年卷期：v.71,no.23(December 1, 1999)
- ISSN：1520-6882
文摘
A computational simulation of the oxidation of chemicalspecies inside a metal emitter electrospray ion source,in the context of electrospray mass spectrometry (ES-MS),has been developed. The analysis code employs a boundary integral method for the solution of the Laplace equation for the electric potential and current and incorporatesstandard activation and concentration polarization functions for the redox-active species in the system to definethe boundary conditions. This paper provides a demonstration of the capability of this simulation method. Dueto the approximate nature of some of the input data, andcertain simplifying assumptions, the present results mustbe considered semiquantitative. The specific system modeled consisted of a 100-
tities/mgr.gif">m-i.d., inert metal capillary ESemitter and a spray solution composed of an analytedissolved in CH3CN/H2O (90/10 v/v). Variable parameters included the concentration (i.e., 5.0, 10, 20, and50 tities/mgr.gif">M) of the easily oxidized analyte ferrocene (Fc,dicyclopentadienyl iron) in the solution, and solutionconductivities of 1.9, 3.8, and 7.6 × 10-7 
-1/cm, withan operational flow rate of 5.0 tities/mgr.gif">L/min and ES currentson the order of 0.05 tities/mgr.gif">A. Under these defined conditions,the two most prominent reactions at the emitter metal/solution interface were assumed to be H2O oxidation(2H2O = O2 + 4H+ + 4e-) and ferrocene oxidation (Fc =Fc+ + e-). Using this model, it was possible to predictthe interfacial potentials, as well as the current densityfor each of the reactions, as a function of axial positionfrom the emitter spray tip back upstream, under thevarious operational conditions. The simulations show thatthe majority of the current from the redox reactions isgenerated within a 200-300-tities/mgr.gif">m region near the spraytip. The lower the value of E0 for a specific reaction, thefurther upstream from the tip the reaction extends.
tities/mgr.gif">m-i.d., inert metal capillary ESemitter and a spray solution composed of an analytedissolved in CH3CN/H2O (90/10 v/v). Variable parameters included the concentration (i.e., 5.0, 10, 20, and50 tities/mgr.gif">M) of the easily oxidized analyte ferrocene (Fc,dicyclopentadienyl iron) in the solution, and solutionconductivities of 1.9, 3.8, and 7.6 × 10-7 -1/cm, withan operational flow rate of 5.0 tities/mgr.gif">L/min and ES currentson the order of 0.05 tities/mgr.gif">A. Under these defined conditions,the two most prominent reactions at the emitter metal/solution interface were assumed to be H2O oxidation(2H2O = O2 + 4H+ + 4e-) and ferrocene oxidation (Fc =Fc+ + e-). Using this model, it was possible to predictthe interfacial potentials, as well as the current densityfor each of the reactions, as a function of axial positionfrom the emitter spray tip back upstream, under thevarious operational conditions. The simulations show thatthe majority of the current from the redox reactions isgenerated within a 200-300-tities/mgr.gif">m region near the spraytip. The lower the value of E0 for a specific reaction, thefurther upstream from the tip the reaction extends.