Matrix-assisted laser desorption electrospray ionization

Matrix-assisted laser desorption electrospray ionization (MALDESI) is an ambient ionization technique which combines the benefits of electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI). MALDESI was introduced in 2006 as the first hybrid ionization source combining laser ablation and electrospray post-ionization using a resonantly excited matrix (endogenous or exogenous). An infrared (IR) or ultraviolet (UV) laser can be utilized in MALDESI in order to resonantly excite an endogenous or exogenous matrix. The term ‘matrix’ refers to any molecule that is present in large excess and absorbs the energy of the laser, facilitating desorption of analyte molecules. The original MALDESI design was implemented using organic matrices, similar to those used in MALDI, along with a UV laser. The more recent MALDESI source uses a thin layer of ice as the energy-absorbing matrix that is resonantly excited using a mid-infrared (IR) laser. Matrix-assisted laser desorption electrospray ionization (MALDESI) is an ambient ionization technique which combines the benefits of electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI). MALDESI was introduced in 2006 as the first hybrid ionization source combining laser ablation and electrospray post-ionization using a resonantly excited matrix (endogenous or exogenous). An infrared (IR) or ultraviolet (UV) laser can be utilized in MALDESI in order to resonantly excite an endogenous or exogenous matrix. The term ‘matrix’ refers to any molecule that is present in large excess and absorbs the energy of the laser, facilitating desorption of analyte molecules. The original MALDESI design was implemented using organic matrices, similar to those used in MALDI, along with a UV laser. The more recent MALDESI source uses a thin layer of ice as the energy-absorbing matrix that is resonantly excited using a mid-infrared (IR) laser. The IR-MALDESI source can be used for mass spectrometry imaging (MSI), a technique using MS data collected over the sample area to visualize the spatial distribution of specific analyte molecules. A versatile IR-MALDESI MSI source was designed and implemented, which is currently coupled to a high resolving power hybrid Quadrupole-Orbitrap mass spectrometer. The source has single- or multi-shot capabilities with adjustable laser fluence, repetition rate, as well as the delay between the laser trigger and MS ion accumulation. The sample plate and moving components are enclosed in a nitrogen purged enclosure where ambient ions and relative humidity can be regulated. A water cooled Peltier thermoelectric plate is used to control the sample temperature (−10 °C to 80 °C).