DART source

Penning ionization is a dominant reaction when nitrogen or neon is used in the DART source. Nitrogen or neon ions are effectively removed by electrostatic lenses and are not observed in the background mass spectrum. When helium is used, the dominant positive-ion formation mechanism involves the formation of ionized water clusters followed by proton transfer reactions. Negative-ion formation occurs by production of electrons by Penning ionization or by surface Penning ionization ... 

Cutaway view of a DART source. Discharge is produced in the first chamber and the gas then flows into a second chamber where the ions can be discharged. The gas flows through a tube that can optionally be heated and then flows out to the sample through a grid that allows removal of ions of opposite polarity. From Cody R.B., Laramee J.A. and Dupont Durst H., Anal. Chem., 77, 2297-2302, 2005. Reprinted, with permission. 

Metastable helium atoms or nitrogen molecules are extracted from the plasma and directed to a sample surface, where Penning ionization makes product ions that can be analyzed by mass spectrometry or IMS. DART sources have been used to ionize a number of classes of compounds as solids or adsorbed directly onto a variety of surfaces. 

FIGURE 2.18 Direct analysis in real time (DART) source. 

DART is easy to use and rapid. To release ions from the surface simply requires placing the samples in the flow of the excited gas atoms. As an example, there is an often heard rumor that U.S. doUar bills that have been in circulation will inevitably be contaminated with cocaine. One of the authors (J.G.) placed a 1 bill in a DART source linked to a time-of-flight analyzer. An ion was immediately observed that was within 5 ppm of tniz 304.1585 Da corresponding to the [M + H]+ of cocaine. 

Direct Analysis in Real Time (the DART Source)... 

Figure 9.10 Diagram of the DART source. (Used with permission from Ion Sense, www.ionsense.com.)...

Isoflavones Soybeans Orbitrap Dart source (APCI) Positive 5 [93] -< V)... 

Various ionization sources are employed in the analysis of explosives by MS. APCI is used with GC-MS, LC-MS, and LC-MS/MS systems for explosives analysis [200-204] this source is chosen because lower LOD can be found with APCI over El sources. However, El remains the ionization source used most often in GC-MS analyses of explosives [12,134-137,139-143,205], DESI, desorption atmospheric pressure chemical ionization (DAPCI), and direct analysis in real time (DART) sources are used to detect explosives, including emerging explosive threats like TATP and as part of field-deployable MS systems [163,206-209],... 

Fig. 13.18. Cutaway view of the DART source. The emanatiag gas effects ionization of sample independent of its state of aggregation. Reproduced from Ref. [2] with permission. The American Chemical Society, 2005.

Fig. 13.19. Commercial DART source. Here it is used for the analysis of volatiles from a garlic clove. The sample is simply held in the open gap between the metastable atom source lower right part) and the orifice of the API interface upper left). Photograph by courtesy ofJEOLUSA.

FIGURE 3.5 Schematic representation of a direct analysis in real time (DART) source. (From Petucci, C. et al.. Analytical Chemistry 79, (2007) 5064.)... 

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