page_title: Desorption electrospray ionization
section_title: Ionization efficiency
hierarchical_section_title: Desorption electrospray ionization / Ionization efficiency
caption_attribution_description: English: Side view of DESI ion source along with a table containing typical values for the geometric parameters.
context_page_description: Desorption electrospray ionization is an ambient ionization technique that can be coupled to mass spectrometry for chemical analysis of samples at atmospheric conditions. Coupled Ionization sources-MS systems are popular in chemical analysis because the individual capabilities of various sources combined with different MS systems allow for chemical determinations of samples. DESI employs a fast-moving charged solvent stream, at an angle relative to the sample surface, to extract analytes from the surfaces and propel the secondary ions toward the mass analyzer. This tandem technique can be used to analyze forensics analyses, pharmaceuticals, plant tissues, fruits, intact biological tissues, enzyme-substrate complexes, metabolites and polymers. Therefore, DESI-MS may be applied in a wide variety of sectors including food and drug administration, pharmaceuticals, environmental monitoring, and biotechnology.
context_section_description: The ionization efficiency of DESI is complex and depends on several parameters such as, surface effects, electrospray parameters, chemical parameters and geometric parameters. Surface effects include chemical composition, temperature and electric potential applied.  Electrospray parameters include electrospray voltage, gas and liquid flow rates.
  Chemical parameters refers to the sprayed solvent composition, e.g. addition of NaCl.  Geometric parameters are α, β, d₁ and d₂ (see figure on the right).
  Furthermore, α and d₁ affect the ionization efficiency, while β and d₂ affect the collection efficiency.  Results of a test performed on a variety of molecules to determine optimal α and d1 values show that there are two sets of molecules: high molecular weight (proteins, peptides, oligosaccharide etc.) and low molecular weight (diazo dye, stereoids, caffeine, nitroaromatics etc.).  The optimal conditions for the high molecular weight group are high incident angles (70-90°) and short d₁ distances (1–3 mm).  The optimal conditions for the low molecular weight group are the opposite, low incident angles (35-50°) and long d₁ distances (7–10 mm).  These test results indicate that each group of molecules has a different ionization mechanism; described in detail in the Principle of operation section.
  The sprayer tip and the surface holder are both attached to a 3D moving stage which allow to select specific values for the four geometric parameters: α, β, d₁ and d₂.
caption: Side view of DESI ion source along with a table containing typical values for the geometric parameters
exif: {}