Desorption Electrospray Ionization (DESI)
This proprietary technology was first published by Dr. R. Graham Cooks' group in Science (Mass Spectrometry Sampling Under Ambient Conditions with Desorption Electrospray Ionization, Science, 2004, 306, 471-473). The diagram below shows a representation of the component parts of DESI and how an Omni Spray® ion source would interface with a standard mass spectrometer.
Desorption Electrospray Ionization (DESI) is carried out by directing charged droplets produced from a pneumatically-assisted electrospray onto a surface to be analyzed at atmospheric conditions. Ions of chemical species present on the surface are produced through the interaction of the charged droplets and the sample. The resulting mass spectra are similar to ESI mass spectra. The composition of the spray solvent, the gas flow rate, the magnitude of the applied voltage, the impact angle, as well as, various distances in aligning the spray with respect to the surface and inlet of the mass spectrometer are variables that can be studied to achieve optimal performance.
Using DESI, high quality mass spectra have already been obtained for a wide range of molecules by directly interrogating a diverse range of surfaces. For example, explosive agents, chemical warfare simulants, amino acids, peptides, proteins, commercially available drug molecules, alkaloids, terpenoids and steroids have all been successfully ionized using DESI. These molecules have been ionized from a diverse range of surfaces (conducting as well as insulating) such as plant tissues, human skin, liquid blood, dried blood spots, urine, as well as from a wide range of inert materials such as polytetrafluoroethylene (PTFE), nitrile gloves, leather belts, pharmaceutical tablets, and many more surfaces that we interact with in our everyday lives.
In summary, the benefits of Desorption Electrospray Ionization include the following:
- DESI is a DIRECT sampling method that requires absolutely no sample preparation
- DESI operates in the atmosphere under ambient conditions
- DESI is a "sensitive" and "gentle" ionization method for the analysis or interrogation of all types of surfaces
- DESI produces electrospray-like spectra
- DESI is effective for both organic and biological compounds
- DESI is effective for polar and non-polar molecules
- DESI allows for in situ analysis of biological tissues and other fragile surfaces
Applications
- Understanding Omni Spray Ion Source Operating Parameters
- Direct ID of Antioxidant on LDPE Using DESI and Accurate Mass Spectrometry on Waters LCT Premier
- The Effect of Nebulizing Gas Pressure, Volumetric Flow Rate and Tip to Surface Distance on Spot Size in DESI-MS
- Mass Spectrometry Imaging Using Desorption Electrospray Ionization