Desorption electrospray ionization in a small pressure-tight enclosure.

Desorption electrospray ionization (DESI) is made easier to implement, more robust, and exposure of the analyst to the sample is reduced by a novel DESI interface. This features a small, pressure-tight enclosure with fixed spatial relationships between the sprayer, surface, and sampling capillary. There is no loss in signal using this configuration, which provides improved safety and ease of use. Performance is largely independent of the geometrical configuration of the spray and inlet. Enclosed DESI sources with the incident and collection capillaries set at various angles were compared to the conventional optimized geometry open DESI source. Comparable results were obtained in all cases for typical proteins, peptides, and small molecules. With the spray and collection capillaries set parallel and at an angle perpendicular to the surface, the new DESI source allows for easy and direct analysis of the contents of standard 96-well plates. The effects of various operating parameters for the new source such as applied spray potential, liquid and gas flow rates, and enclosure material were investigated.