Abstract
Ions that are observed in a mass spectrum obtained with electrospray mass spectrometry can be assumed to originate preferentially from ions that have a high distribution to the surface of the charged droplets. In this study, a relation between chromatographic retention and electrophoretic mobility to the ion distribution (derived from measured signal intensities in mass spectra and electrospray current) within electrosprayed droplets for a series of tetraalkylammonium ions, ranging from tetramethyl to tetrapentyl, is presented. Chromatographic retention in a reversed-phase system was taken as a measure of the analyte’s surface activity, which was found to have a large influence on the ion distribution within electrosprayed droplets. In addition, different transport mechanisms such as electrophoretic migration and diffusion can influence the surface partitioning coefficient. The viscosity of the solvent system is affected by the methanol content and will influence both diffusion and ion mobility. However, as diffusion and ion mobility are proportional to each other, we have, in this study, chosen to focus on the ion mobility parameter. It was found that the influence of ion mobility relative to surface activity on the droplet surface partitioning of analyte ions decreases with increasing methanol content. This effect is most probably coupled to the decrease in droplet size caused by the decreased surface tension at increasing methanol content. The same observation was made upon increasing the ionic strength of the solvent system, which is also known to give rise to a decreased initial droplet size. The observed effect of ionic strength on the droplet surface partitioning of analyte ions could also be explained by the fact that at higher ionic strength, a larger number of ions are initially closer to the droplet surface and, thus, the contribution of ionic transport from the bulk liquid to the liquid/air surface interface (jet and droplet surface), attributable to migration or diffusion will decrease.
Article PDF
Similar content being viewed by others
Avoid common mistakes on your manuscript.
References
Tang, L.; Kebarle, P. Effect of the Conductivity of the Electrosprayed Solution on the Electrospray Current. Factors Determining Analyte Sensitivity in Electrospray Mass Spectrometry. Anal. Chem. 1991, 63, 2709–2715.
Iribarne, J. V.; Thomson, B. A. On the Evaporation of Small Ions from Charged Droplets. J. Chem. Phys. 1976, 64, 2287–2294.
Tang, L.; Kebarle, P. Dependence of Ion Intensity in Electrospray Mass Spectrometry on the Concentration of the Analytes in the Electrosprayed Solution. Anal. Chem. 1993, 65, 3654–3668.
Enke, C. G. A Predictive Model for Matrix and Analyte Effects in Electrospray Ionization of Singly-Charged Ionic Analytes. Anal. Chem. 1997, 69, 4885–4893.
Cech, N. B.; Krone, J. R.; Enke, C. G. Predicting Electrospray Response from Chromatographic Retention Times. Anal. Chem. 2001, 73, 208–213.
Zhou, S.; Cook, K. D. A. Mechanistic Study of Electrospray Mass Spectrometry: Charge Gradients Within Electrosprayed Droplets and Their Influence on Ion Response. J. Am. Soc. Mass Spectrom. 2001, 12, 206–214.
Sjöberg, P. J. R.; Bökman, C. F.; Bylund, D.; Markides, K. E. A Simple Method for Determination of Ion Distribution Within Electrospray Droplets. Anal. Chem. 2001, 73, 23–28.
Sjöberg, P. J. R.; Bökman, C. F.; Bylund, D.; Markides, K. E. Factors Influencing the Determination of Analyte Ion Surface Partitioning Coefficients in Electrosprayed Droplets. J. Am. Soc. Mass Spectrom. 2001, 12, 1001–1010.
Bruins, A. P. 1997; Cole, R. B., Ed.; In Electrospray Ionization Mass Spectrometry, Fundamentals, Instrumentation and Applications; pp 107–136. Wiley-Interscience: New York,
Harris, D. C. In Quantitative Chemical Analysis; W. H. Freeman and Company: New York, 2002.
Baczek, T.; Markuszewski, M.; Kaliszan, R.; van Straten, M. A.; Claessens, H. A. Linear and Quadratic Relationships Between Retention and Organic Modifier Content in Eluent in Reversed Phase High-Performance Liquid Chromatography: A Systematic Comparative Statistical Study. J. High Resolut. Chromatogr. 2000, 23, 667–676.
Atkins, P. W. In Physical Chemistry; Oxford University Press: Oxford, 1986.
Snyder, L. R.; Kirkland, J. J.; Glajch, J. L. In Practical HPLC Method Development; John Wiley and Son, Inc.: New York, 1997; p 726.
Pospichehal, J.; Gebauer, P.; Bocek, P. Measurement of Mobilities and Dissociation Constants by Capillary Isotachophoresis. Chem. Rev. 1989, 89, 419–430.
Cech, N. B.; Enke, C. G. Effect of Affinity for Droplet Surface on the Fraction of Analyte Molecules Charged During Electrospray Droplet Fission. Anal. Chem. 2001, 73, 4632–4639.
Constantopoulos, T. L.; Jackson, G. S.; Enke, C. G. Effect of Salt Concentration on Analyte Response Using Electrospray Ionization Mass Spectrometry. J. Am. Soc. Mass Spectrom. 1999, 10, 625–634.
Smith, D. P. H. The Electrohydrodynamic Atomization of Liquids. IEEE Trans. Ind. Appl. 1986, IA-22, 527–535.
de la Mora, J. Fernandez; Loscertales, I. G. The Current Emitted by Highly Conducting Taylor Cones. J. Fluid Mech. 1994, 260, 155–184.
Rosell-Llompart, J.; Fernandez de la Mora, J. Generation of Monodisperse Droplets 0.3 to 4 um in Diameter from Electrified Cone-Jets of Highly Conducting and Viscous Liquids. J. Aerosol Sci. 1994, 25, 1093–1119.
Loscertales, I. G.; Fernandez de la Mora, J. Experiments on the Kinetics of Field Evaporation of Small Ions from Droplets. J. Chem. Phys. 1995, 103, 5041–5059.
Kim, J. H.; Nakajima, T. Aerodynamic Influences on Droplet Atomization in an Electrostatic Spray. JSME Int. J. Series B 1999, 42, 224–229.
Author information
Authors and Affiliations
Corresponding author
Additional information
Published online January 25, 2006
Rights and permissions
About this article
Cite this article
Bökman, C.F., Bylund, D., Markides, K.E. et al. Relating chromatographic retention and electrophoretic mobility to the ion distribution within electrosprayed droplets. The official journal of The American Society for Mass Spectrometry 17, 318–324 (2006). https://doi.org/10.1016/j.jasms.2005.11.006
Received:
Revised:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1016/j.jasms.2005.11.006