A brief overview of the present status of the mechanisms involved in electrospray mass spectrometry.

A brief account of the mechanisms by which ions in solution are converted to ions in the gas phase is given on the basis of information available in the literature and the four companion articles on electrospray mass spectrometry (ESMS) in this issue. The following stages/phenomena are described: (a) production of the charged droplets at the ES capillary tip; (b) evolution of the charged droplets due to solvent evaporation and droplet fission caused by Coulombic repulsion of the charges on the droplets; production of the gas phase ion from very small charged droplets by the charge residue model (CRM) or the ion evaporation method (IEM); (c) dependence of the sensitivity in ESMS on the chemical nature of the analyte and its concentration as well as on the concentration of other electrolytes that are present in the solution; qualitative predictions on the sensitivity of the analyte based on the surface activity of the analyte ions; (d) relationship between ions produced in the gas phase and original ions present in the solution; and (e) globular proteins. Much of the information presented in (a)-(e) has been available for some time in the literature. However some significant advances are relatively recent. Recent results by de la Mora and co-workers, including their contribution in this Special Feature, provide very strong evidence that small ions (in distinction from macroions such as bio-macroions) are produced by IEM. On the other hand, macroions and particularly the polyprotonated globular proteins are produced by CRM. Also noteworthy is the development of an equation by Enke with which the observed relative ion signal intensities of the gas-phase ions produced can be predicted on the basis of the ion concentration in solution over a wide concentration range. The recognition that the sensitivity of organic analyte ions can be qualitatively predicted on the basis of the hydrophilicity or hydrophobicity of the part of the molecule that is not part of the charged (ionic) group and affects the surface activity of the ionic species is also noteworthy and a very useful relatively recent development.

[1]  G. J. Berkel.  Electrolytic deposition of metals on to the high-voltage contact in an electrospray emitter: implications for gas-phase ion formation. , 2000 .

[2]  C. Enke,et al.  Importance of gas-phase proton affinities in determining the electrospray ionization response for analytes and solvents. , 2000, Journal of mass spectrometry : JMS.

[3]  R. Cole,et al.  Some tenets pertaining to electrospray ionization mass spectrometry. , 2000, Journal of mass spectrometry : JMS.

[4]  Gamero-Castano,et al.  Kinetics of small ion evaporation from the charge and mass distribution of multiply charged clusters in electrosprays , 2000, Journal of mass spectrometry : JMS.

[5]  J. Mora,et al.  Electrospray ionization of large multiply charged species proceeds via Dole’s charged residue mechanism , 2000 .

[6]  M. Gamero-Castaño,et al.  Mechanisms of electrospray ionization of singly and multiply charged salt clusters , 2000 .

[7]  R. Cole,et al.  Charged residue versus ion evaporation for formation of alkali metal halide cluster ions in ESI , 2000 .

[8]  P. Kebarle,et al.  On the mechanisms by which the charged droplets produced by electrospray lead to gas phase ions , 2000 .

[9]  R. Hettich.  Formation and characterization of iron-oligonucleotide complexes with matrix-assisted laser desorption/ionization Fourier transform ion cyclotron resonance mass spectrometry , 1999, Journal of the American Society for Mass Spectrometry.

[10]  P. Kebarle,et al.  FORMATION, ACIDITY AND CHARGE REDUCTION OF THE HYDRATES OF DOUBLY CHARGED IONS M2+ (BE2+, MG2+, CA2+, ZN2+) , 1999 .

[11]  E. P. Hunter,et al.  Evaluated Gas Phase Basicities and Proton Affinities of Molecules: An Update , 1998 .

[12]  C. Enke,et al.  A predictive model for matrix and analyte effects in electrospray ionization of singly-charged ionic analytes. , 1997, Analytical chemistry.

[13]  M. Jarrold,et al.  High resolution ion mobility measurements for gas phase proteins: correlation between solution phase and gas phase conformations , 1997 .

[14]  Robert K. Boyd,et al.  ‘Wrong‐way‐round’ Electrospray Ionization of Amino Acids , 1997 .

[15]  David E. Clemmer,et al.  Disulfide-Intact and -Reduced Lysozyme in the Gas Phase: Conformations and Pathways of Folding and Unfolding , 1997 .

[16]  M. Jarrold,et al.  PROTEIN STRUCTURE IN VACUO : GAS-PHASE CONFORMATIONS OF BPTI AND CYTOCHROME C , 1997 .

[17]  A. Jaffrezic,et al.  Correlation Between Solvation Energies and Electrospray Mass Spectrometric Response Factors. Study by Electrospray Mass Spectrometry of Supramolecular Complexes in Thermodynamic Equilibrium in Solution , 1996 .

[18]  P. Schnier,et al.  On the maximum charge state and proton transfer reactivity of peptide and protein ions formed by electrospray ionization , 1995, Journal of the American Society for Mass Spectrometry.

[19]  I. G. Loscertales,et al.  Experiments on the kinetics of field evaporation of small ions from droplets , 1995 .

[20]  R. Cole,et al.  Mechanistic Interpretation of the Dependence of Charge State Distributions on Analyte Concentrations in Electrospray Ionization Mass Spectrometry , 1995 .

[21]  K. Hiraoka,et al.  Do the Electrospray Mass Spectra Reflect the Ion Concentrations in Sample Solution , 1995 .

[22]  R. Cole,et al.  Effect of Solution Ionic Strength on Analyte Charge State Distributions in Positive and Negative Ion Electrospray Mass Spectrometry , 1994 .

[23]  R. Cole,et al.  Disparity between solution‐phase equilibria and charge state distributions in positive‐ion electrospray mass spectrometry , 1994 .

[24]  F. Tureček,et al.  Acidity Determination in Droplets Formed by Electrospraying Methanol-Water Solutions , 1994 .

[25]  A. Gomez,et al.  Charge and fission of droplets in electrostatic sprays , 1994 .

[26]  P. Kebarle,et al.  Dependence of ion intensity in electrospray mass spectrometry on the concentration of the analytes in the electrosprayed solution , 1993 .

[27]  S. Thiebes,et al.  Cluster ion formation in thermospray mass spectrometry of ammonium salts , 1993 .

[28]  P. Kebarle,et al.  Negative ion electrospray mass spectrometry of nucleotides: ionization from water solution with SF6 discharge suppression , 1993, Journal of the American Society for Mass Spectrometry.

[29]  J. Mora,et al.  The effect of charge emission from electrified liquid cones , 1992, Journal of Fluid Mechanics.

[30]  C. Fenselau,et al.  Electrospray analysis of proteins: A comparison of positive-ion and negative-ion mass spectra at high and low pH , 1992 .

[31]  P. Kebarle,et al.  Effect of the conductivity of the electrosprayed solution on the electrospray current. Factors determining analyte sensitivity in electrospray mass spectrometry , 1991 .

[32]  P. Kebarle,et al.  Electrospray mass spectrometry of methanol and water solutions suppression of electric discharge with SF6 gas , 1991, Journal of the American Society for Mass Spectrometry.

[33]  P. Kebarle,et al.  Mechanism of electrospray mass spectrometry. Electrospray as an electrolysis cell , 1991 .

[34]  Michael G. Ikonomou,et al.  Electrospray-ion spray: a comparison of mechanisms and performance , 1991 .

[35]  Richard D. Smith,et al.  Principles and practice of electrospray ionization—mass spectrometry for large polypeptides and proteins , 1991 .

[36]  B. Ganem,et al.  Observation of noncovalent enzyme-substrate and enzyme-product complexes by ion-spray mass spectrometry , 1991 .

[37]  B. Ganem,et al.  Detection of noncovalent receptor-ligand complexes by mass spectrometry , 1991 .

[38]  P. Kebarle,et al.  Studies of alkaline earth and transition metal M++ gas phase ion chemistry , 1990 .

[39]  Michael G. Ikonomou,et al.  Investigations of the electrospray interface for liquid chromatography/mass spectrometry , 1990 .

[40]  M. Mann,et al.  Electrospray ionization for mass spectrometry of large biomolecules. , 1989, Science.

[41]  F. Röllgen,et al.  Desolvation of ions and molecules in thermospray mass spectrometry , 1989 .

[42]  I. Hayati,et al.  Investigations into the mechanisms of electrohydrodynamic spraying of liquids. I: Effect of electric field and the environment on pendant drops and factors affecting the formation of stable jets and atomization , 1987 .

[43]  David P. H. Smith,et al.  The Electrohydrodynamic Atomization of Liquids , 1986, IEEE Transactions on Industry Applications.

[44]  J. V. Iribarne,et al.  Field induced ion evaporation from liquid surfaces at atmospheric pressure , 1979 .

[45]  P. Kebarle,et al.  Binding energies and stabilities of potassium ion complexes from studies of the gas phase ion equilibriums K+ + M = K+M , 1976 .

[46]  P. Kebarle,et al.  Binding energies and stabilities of potassium ion complexes with ethylene diamine and dimethoxyethane (glyme) from measurements of the complexing equilibria in the gas phase , 1976 .

[47]  J. V. Iribarne,et al.  On the evaporation of small ions from charged droplets , 1976 .

[48]  P. Kebarle,et al.  Hydration of the alkali ions in the gas phase. Enthalpies and entropies of reactions M+(H2O)n-1 + H2O = M+(H2O)n , 1970 .

[49]  R. C. Mobley,et al.  Molecular Beams of Macroions , 1968 .