An improvement to Desorption Electrospray Ionization (DESI), the process of creating ions directly from sample surfaces for mass spectrometric (MS) analysis by impinging a liquid spray onto the surface. The improvement is brought about by enclosing the spray and sample surface and MS-inlet capillary in a pressure tight enclosure. The invention includes methods of sampling a larger or smaller area of surface by impacting and collecting droplets from such an area. The invention allows DESI to be performed without need for careful control of the geometry of the sprayer and MS-inlet capillary positions and angles relative to the sample surface.