Abstract: A method of isolating a charged, especially proteinaceous, compound comprises providing a prepared sample of the compound in solution, placing the prepared sample in contact with a membrane so limited in effective adsorptive surface area as to enable reversible binding to the membrane of the charged compound in the sample presented to the adsorptive surface such that solvent is removable therefrom and the charged compound is left substantially reversibly bound thereto, and eluting the compound from the membrane. Eluted compounds can then be directly subjected to mass spectrometric analysis for charcterisation of, for example, individual peptides.