DESI mass spectrometry

J. M. Wiseman, D. R. Ifa, Q. Song and R. G. Cooks, Tissue imaging at atmospheric pressure using Desorption Electrospray Ionization (DESI) mass spectrometry, Angew. Chem. Int. Edn, 45, 7188 7192 (2006). 

Weston DJ (2010) Ambient ionization mass spectrometry current understanding of mechanistic theory analytical performance and application areas. Analyst 135 661-668 Wiseman JM, Evans CA, Bowen CL, Kennedy JH (2010) Direct analysis of dried blood spots utilizing desorption electrospray ionization (DESI) mass spectrometry. Analyst 135 720-725... 

Ifa DR, Gumaelius LM, Eberlin LS, et al. (2007) Forensic analysis of inks by imaging desorption eleetrospray ionization (DESI) mass spectrometry. Analyst 132 461-7. 

Manicke, N.E., Wiseman, J.M., Ifa, D.R. and Cooks, R.G. (2008) Desorption electrospray ionization (DESI) mass spectrometry and tandem mass spectrometry (MS/MS) of phosphohpids and sphingolipids Ionization, addnct formation, and fragmentation. J. Am. Soc. Mass Spectrom. 19, 531-543. 

Over the years, a lot of desorption ionization techniques have been introduced to MS, such as plasma desorption, field desorption, laser desorption, secondary ion mass spectrometry, fast atom bombardment, matrix assisted laser desorption and desorption electrospray ionization. Most of them are actually no longer used. In the following paragraphs, both matrix assisted laser desorption (MALDI) and desorption electrospray ionization (DESI) will be discussed. 

Z. Takats, J. M. Wiseman and R. G. Cooks, Ambient mass spectrometry using desorption electrospray ionization (DESI) instmmentation, mechanisms and applications in forensics, chemistry, and biology, J. Mass Spectrom., 40, 1261 1275 (2005). 

DGE a AC AMS APCI API AP-MALDI APPI ASAP BIRD c CAD CE CF CF-FAB Cl CID cw CZE Da DAPCI DART DC DE DESI DIOS DTIMS EC ECD El ELDI EM ESI ETD eV f FAB FAIMS FD FI FT FTICR two-dimensional gel electrophoresis atto, 10 18 alternating current accelerator mass spectrometry atmospheric pressure chemical ionization atmospheric pressure ionization atmospheric pressure matrix-assisted laser desorption/ionization atmospheric pressure photoionization atmospheric-pressure solids analysis probe blackbody infrared radiative dissociation centi, 10-2 collision-activated dissociation capillary electrophoresis continuous flow continuous flow fast atom bombardment chemical ionization collision-induced dissociation continuous wave capillary zone electrophoresis dalton desorption atmospheric pressure chemical ionization direct analysis in real time direct current delayed extraction desorption electrospray ionization desorption/ionization on silicon drift tube ion mobility spectrometry electrochromatography electron capture dissociation electron ionization electrospray-assisted laser desorption/ionization electron multiplier electrospray ionization electron transfer dissociation electron volt femto, 1CT15 fast atom bombardment field asymmetric waveform ion mobility spectrometry field desorption field ionization Fourier transform Fourier transform ion cyclotron resonance... 

R. G. Ambient mass spectrometry using desorption electrospray ionization (DESI) instrumentation, mechanisms and applications in forensics, chemistry, and biology. 

The ionization methods reported for IMS included MALDI [41,76-80], Secondary Ion Mass Spectrometry (SIMS) [19, 81-86], Matrix-enhanced (ME)-SIMS [87, 88], Desorption Electrospray Ionization (DESI) [89-99], Nanostructure Initiator Mass Spectrometry (NIMS) [100-102], Atmospheric Pressure Infrared MALDI Mass Spectrometry (AP-IR-MALDI-MS) [103], Laser Ablation-inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) [104-106], Laser Desorption Postionization (LDPI) [107], Laser Ablation Electrospray Ionization Mass Spectrometry (LAESI) [108, 109], and Surface-assisted Laser Desorption/ioniza-tion Mass Spectrometry (SALDI) [110-112], Another method was called probe electrospray ionization (PESI) that was used for both liquid solution and the direct sampling on wet samples. 

Ifa D, Wiseman J, Song Q, Cooks G (2007) Development of capabilities for imaging mass spectrometry under ambient conditions with desorption electrospray ionization (DESI). Int J Mass Spectrom 259 8-15. doi 10.106/j.ijms.2006.08.003... 

Takats Z, Kobliha V, Sevcik K, Novak P, Kruppa G, Lemr K, Havlicek V (2008) Characterization of DESI-FTICR mass spectrometry-from ECD to accurate mass tissue analysis. J Mass Spectrom 43 196-203. doi 10.1002/jms.l285... 

Techniques for the Ionization of Molecules The measurability of molecules by MSI is enabled through the local desorption and ionization of the molecules from a surface. In theory, all types of molecules that can undergo these two chemical processes can be measured. Many techniques have been developed or adapted to achieve desorption and ionization of molecules from surfaces, but three different desorption/ioniza-tion techniques made their way to commercially available products. The acronyms of these technologies are desorption electrospray ionization (DESI), MALDI, and secondary ion mass spectrometry (SIMS). The principles of these three methods and a comparison of their possibilities and limitations are outlined throughout this section and summarized in Figure 1 and Table 2, respectively. 

PE Andren, S Lin, RN Caprioli. Microdialysis/mass spectrometry. In DM Desi-derio, ed. Mass Spectrometry Clinical and Biomedical Applications. Vol. 2. New York Plenum Press, 1992, pp 237—253. 

One of the most significant developments in mass spectrometry in the recent years is the introduction of a new class of ionization methods where samples in either solid or liquid state can be directly ionized in their native environment under ambient conditions (rather than inside a mass spectrometer) without any sample preparation. This new class of ionization methods is often referred to as ambient ionization methods [1,2], Because these methods generally ionize analytes on the surface or near the surface of the samples at atmospheric pressure, they have also been called atmospheric pressure surface sampling/ionization methods or direct/open air ionization methods [3], Since the first reports on ambient ionization with desorption electrospray ionization (DESI) [4] and direct analysis in real time (DART) [5], numerous reports have been published on the applications of these new ionization methods as well as the introduction of many related ambient ionization methods such as desorption atmospheric pressure chemical ionization (DAPCI) [6], atmospheric solid analysis probe (ASAP) [7], and electrospray-assisted laser desorption/ionization (ELDI) [8], Recently, two reviews of the various established and emerging ambient ionization methods have been published [2,3],... 

In addition to some early applications in bioanalysis, ambient ionization mass spectrometry has been used as an imaging tool to study drug distribution in tissue sections. Most of the work reported so far involved the use of DESI as the ambient ionization method. Compared to other mass spectrometry-based tissue imaging techniques such as MALDI and SIMS, DESI allows tissue samples to be analyzed under ambient conditions without sample preparation, which simplifies the procedure and prevents the redistribution of analytes during matrix deposition. A major drawback of DESI as an imaging tool is its relatively low spatial resolution (typically 250 pm) and therefore cannot be used for cellular or subcellular imaging. 

The reason for writing this second edition is simple—science marches on and there are new topics and areas of interest that did not exist in 2003, when the first edition of this book was written. We now have UPLC and Orbitraps as well as DESI and DART to name a few of the new instruments and techniques that are now part of our toolset for using mass spectrometry for drug metabolism studies. This second edition is a completely new book with 14 new chapters that were written solely for this edition. While some of the topics are the same as in the first edition, the newly written chapters provide the latest thinking on how best to use mass spectrometry in a drug metabolism setting. 

Two new independently developed techniques called Dart ° (direct analysis in real time) and Desi (desorption electrospray ionisation) are making a huge impact on mass spectrometry. Together they remove the need for sample preparation and vacuum, speed up analysis time and can work in the open air. The sample is held in a gas or liquid stream at room temperature and the impact induces the surface desorption of ions. The ions then continue into the vacuum interface of the MS for analysis. Samples can be hard, soft or even liquid in nature. Ifa et al. have used Desi to image biological samples in two dimensions, recording images of tissue sections and the relative concentrations of molecules therein. Jeol have launched a commercial Dart ion source for non-contact analysis of materials in open air under ambient conditions. 

FIGURE 3.15 Schematic of a typical DESI experiment. (From Weston et al. Direct analysis of pharmaceutical drug formulations using ion mobility spectrometry/quadrupole-time-of-flight mass spectrometry combined with desorption electrospray ionization Anal. Chem. 2005, 77(23), 7572-7580. 

The preparation of samples for mass spectrometric analysis almost always requires recovery of the analyte from a matrix, often followed by further preparative steps prior to introduction of the sample into the ion source. Such destructive processes are unacceptable when the objective is to determine the specific location of a particular compound within a biological sample, e.g., the location of a certain lipid in a tissue, and led to the development of imaging mass spectrometry with MALDI as the ionization method, although DESI is also applicable. 

In ESI, ionization occurs due to electrospray process, whereas in DESI, it is the impact of a beam of ions, neutrals, etc. that causes ionization. Also, DESI is performed in ambient air, whereas ESI in the mass spectrometry ion somce. 

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