Ambient desorption ionization mass spectrometry

Ambient desorption ionization mass spectrometry (MS) allows for the direct analysis of ordinary objects in the open atmosphere of the laboratory or in their natural environment. Analyte desorption usually accompanies the ionization step and these processes are often concerted, multi-step processes. Ambient desorption ionization methods typically require little or no sample preparation, offer a much simplified work flow and deliver unprecedented ease of use to MS analyses. Since the introduction of desorption electrospray ionization (DESI [Z. Takats, J.M. Wiseman, B. Gologan, R.G. Cooks, Science (Washington, D. C.) 306 (2004) 471]) in 2004 and the direct analysis in real time (DART [R.B. Cody, J.A. Laramee, H.D. Durst, Anal. Chem. 77 (2005) 2297]) in 2005, this new field of MS has developed rapidly. Numerous permutations of the various options for analyte desorption and ionization have been demonstrated. Desorption steps, such as momentum transfer, dissolution into ricocheting droplets and thermal desorption, have been combined with ionization steps, including ESI, atmospheric pressure chemical ionization and photo-ionization. The large number of possible combinations of desorption and ionization components that have already been applied is creating a proliferation of techniques and acronyms that is becoming ever more complex. Here, we provide a logical framework for the classification of these related experiments, based on the desorption and ionization processes involved in each.