The solvent shells of cluster ions produced by direct electric field extraction from glycerol/water mixtures

Electric field extraction of gaseous negative ions directly from water/glyc erol solutions by use of a track membrane technique was investigated. The d istributions of numbers of solvent molecules in the extracted cluster ions for different compounds were obtained. It is shown that the extraction mech anism is a direct field-stimulated evaporation of cluster ions from liquid, with a subsequent loss of several solvent molecules in the vacuum. For rel atively simple ions a good correspondence of results was obtained with a co ntinuous medium model. It was found that the number of solvent molecules in a cluster shell, for more complicated ions such as amino acids, is signifi cantly greater than that for halide ions or ions of simple organic acids. A n increase in the number of solvent molecules in the case of amino acid neg ative ions is rationalized in terms of the existence of several charged gro ups, each of which gives an additional contribution to the cluster shell. C opyright (C) 2001 John Wiley & Sons, Ltd.