The possibility of the application of the electromembrane technique for production of ions of biological molecules at atmospheric pressure is demonstrated. This technique has previously only been used for extraction of ions from liquids directly into vacuum. The membrane technique for ion extraction at atmospheric pressure was tested with both time-of-flight and Fourier transform ion cyclotron resonance mass spectrometers. The mass spectra of intact molecular ions obtained from aqueous solutions of peptides and proteins are presented. The possible mechanisms of non-destructive ion extraction are discussed. The new technique is promising for achieving absolute sensitivity (charging every analyte molecule) and for performing spatially-resolved analysis of liquid biological samples.

An approach to the generation of gas phase ions by field extraction from liquid solutions has been investigated. The method uses a polymer membrane with nano-size channels as an interface between the liquid and the atmospheric pressure gas. Ions are produced by dissociation in the polar solvent and secondary ion-molecular reactions in the solution, which fills the channels of the membrane. Field extraction of the ions from the channels is stimulated by pulses of the electric discharge between the membrane and an adjacent electrode in the gas. The gas-phase ions are removed from the extraction zone by air flow and are detected by mass spectrometry. Possibilities of the membrane interface for generation of gas phase ions have been demonstrated from mass spectral investigation curried out for angiotensin II, gramicidin S and cytochrome C solutions. The current kinetics of the membrane ion source has been investigated to elucidate the mechanism of the ion extraction.Keywords track membrane; field extraction of ions; atmospheric membrane ion source

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