page_title: Direct analysis in real time
section_title: Source to analyzer interface
hierarchical_section_title: Direct analysis in real time / Principle of operation / Instrumentation / Source to analyzer interface
caption_attribution_description: English: image of DART ion source
context_page_description: In mass spectrometry, direct analysis in real time is an ion source that produces electronically or vibronically excited-state species from gases such as helium, argon, or nitrogen that ionize atmospheric molecules or dopant molecules. The ions generated from atmospheric or dopant molecules undergo ion-molecule reactions with the sample molecules to produce analyte ions. Analytes with low ionization energy may be ionized directly. The DART ionization process can produce positive or negative ions depending on the potential applied to the exit electrode.
  This ionization can occur for species desorbed directly from surfaces such as currency, tablets, bodily fluids, polymers, glass, plant leaves, fruits & vegetables, clothing, and living organisms. DART is applied for rapid analysis of a wide variety of samples at atmospheric pressure and in the open laboratory environment. It does not need a specific sample preparation, so it can be used for the analysis of solid, liquid and gaseous samples in their native state.
  With the aid of DART, exact mass measurements can be done rapidly with high-resolution mass spectrometers.
context_section_description: Analyte ions are formed at ambient pressure during Penning and chemical ionization.The mass spectrometry analysis, however, takes place at high vacuum condition.  Therefore ions entering the mass spectrometer, first go through a source - to - analyzer interface (vacuum interface), which was designed in order to bridge the atmospheric pressure region to the mass spectrometer vacuum. It also minimizes spectrometer contamination. 
  In the original JEOL atmospheric pressure interface used for DART, ions are directed to the ion guide through  (outer) і  and (inner) іі skimmer orifices by applying a slight potential difference between them: orifice і : 20 V and orifice іі : 5 V.  The alignment of the two orifices is staggered to trap neutral contamination and protect the high-vacuum region. Charged species (ions) are guided to the second orifice through an intermediate cylindrical electrode ("ring lens"), but neutral molecules travel in a straight pathway and are thus blocked from entering the ion guide.  The neutral contamination is then removed by the pump.
  The DART source can be operated in surface desorption mode or transmission mode. In the ordinary surface desorption mode, the sample is positioned in a way, which enables the reactive DART reagent ion stream to flow on to the surface while allowing the flow of desorbed analyte ions into interface. Therefore this mode requires that the gas stream grazes the sample surface and does not block gas flow to the mass spectrometer sampling orifice. In contrast, transmission mode DART (tm-DART) uses a custom-made sample holder and introduces the sample at a fixed geometry.
caption: Schematic diagram of DART-transmission mode
exif: {}