The term Ambient Mass Spectrometry coined by R. Graham Cooks in 2006 is applied to experiments in which MS is used to examine a sample directly in the free ambient environment, where it is simultaneously accessible to other physical or chemical treatment or examination. The new experiments are capable of examining untreated samples in the open atmosphere. Another important feature of ambient mass spectrometric methods is their minimally invasive character. This feature allows the mass spectrometric investigation of delicate samples, and in vivo experiments. Ambient MS methods are obviously destructive, since mass spectrometry is destructive by its nature; however these methods consume only the necessary amount of samples, leaving the major part intact. Ambient MS methods redefine the concept of sample for mass spectrometry. Using these methods, practically any object qualifies as a sample. In this sense, samples subjected to ambient MS are typically in the condensed phase, including adsorbates on surfaces.
The principal method in ambient MS is Desorption Electrospray Ionization (DESI). (see also: Wiki DESI) In the DESI experiment, ions are generated from the sample surface by way of bombardment with high velocity, charged micro-droplets through the atmosphere. The spray impact causes the formation of microscopic liquid layers on the sample surface in which the condensed-phase analyte dissolves. This process is followed by desorption via momentum transfer when additional droplets collide with the liquid layer forcing the dissolved analyte into the gas (atmospheric air) phase in the form of micron-sized droplets. (see also: droplet simulations) The applications of the method are extensive and range from direct tablet analysis for degradation studies or counterfeit ID to the examination of thin-layer chromatography plates and 2D and 3D molecular imaging of biological tissue.
