Desorption electrospray ionization (DESI) is an ambient ionization technique that can be used in mass spectrometry for chemical analysis. It is an atmospheric pressure ion source that ionizes gases, liquids and solids in open air under conditions. It was developed in 2004 by Professor Graham Cooks' group from Purdue University and is now available commercially by Prosolia Inc. DESI is a similar ionization technique to Direct Analysis in Real Time (DART) in its versatility, applications and analysis time.